diff --git a/Cargo.lock b/Cargo.lock
index f25a28a..a1992c0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -6,11 +6,91 @@ version = 3
 name = "aoc2021"
 version = "0.1.0"
 dependencies = [
+ "argh",
  "bounded-vec-deque",
 ]
 
+[[package]]
+name = "argh"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f023c76cd7975f9969f8e29f0e461decbdc7f51048ce43427107a3d192f1c9bf"
+dependencies = [
+ "argh_derive",
+ "argh_shared",
+]
+
+[[package]]
+name = "argh_derive"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "48ad219abc0c06ca788aface2e3a1970587e3413ab70acd20e54b6ec524c1f8f"
+dependencies = [
+ "argh_shared",
+ "heck",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "argh_shared"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38de00daab4eac7d753e97697066238d67ce9d7e2d823ab4f72fe14af29f3f33"
+
 [[package]]
 name = "bounded-vec-deque"
 version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2225b558afc76c596898f5f1b3fc35cfce0eb1b13635cbd7d1b2a7177dc10ccd"
+
+[[package]]
+name = "heck"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6d621efb26863f0e9924c6ac577e8275e5e6b77455db64ffa6c65c904e9e132c"
+dependencies = [
+ "unicode-segmentation",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba508cc11742c0dc5c1659771673afbab7a0efab23aa17e854cbab0837ed0b43"
+dependencies = [
+ "unicode-xid",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38bc8cc6a5f2e3655e0899c1b848643b2562f853f114bfec7be120678e3ace05"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.82"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8daf5dd0bb60cbd4137b1b587d2fc0ae729bc07cf01cd70b36a1ed5ade3b9d59"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
+[[package]]
+name = "unicode-segmentation"
+version = "1.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8895849a949e7845e06bd6dc1aa51731a103c42707010a5b591c0038fb73385b"
+
+[[package]]
+name = "unicode-xid"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8ccb82d61f80a663efe1f787a51b16b5a51e3314d6ac365b08639f52387b33f3"
diff --git a/Cargo.toml b/Cargo.toml
index b6ab0e5..8fcb16a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,3 +7,4 @@ edition = "2018"
 
 [dependencies]
 bounded-vec-deque = "0.1.1"
+argh = "^0.1.6"
diff --git a/rustfmt.toml b/rustfmt.toml
new file mode 100644
index 0000000..b3c83c4
--- /dev/null
+++ b/rustfmt.toml
@@ -0,0 +1 @@
+max_width = 79
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index afa12de..0ff668e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,33 +1,24 @@
 use std::io;
-use std::io::prelude::*;
-use std::env;
-use std::fs::File;
 
-use bounded_vec_deque::BoundedVecDeque;
+use argh::FromArgs;
 
+mod sonar;
+
+#[derive(FromArgs)]
+/// Elvish Submarine Sonar Tracker
+struct Arguments {
+    /// path to input data file
+    #[argh(positional)]
+    input: String,
+
+    /// sliding window size
+    #[argh(option, default = "1")]
+    window: usize,
+}
 
 fn main() -> io::Result<()> {
-    let args: Vec<String> = env::args().collect();
-    let f = File::open(&args[1])?;
-    let buf = io::BufReader::new(f);
-    let mut deque: BoundedVecDeque<i32> = BoundedVecDeque::with_capacity(3, 3);
-    let mut last = -1;
-    let mut count_incr = 0;
-    for line in buf.lines() {
-        if let Ok(l) = line {
-            if let Ok(value) = i32::from_str_radix(&l, 10) {
-                deque.push_back(value);
-            }
-            if deque.is_full() {
-                eprintln!("{:?}", deque);
-                let sum = deque.iter().sum();
-                if last > -1 && sum > last {
-                    count_incr += 1;
-                }
-                last = sum;
-            }
-        }
-    }
+    let args: Arguments = argh::from_env();
+    let count_incr = sonar::count_increases(&args.input, args.window)?;
     println!("number of increases: {}", count_incr);
     Ok(())
 }
diff --git a/src/sonar.rs b/src/sonar.rs
new file mode 100644
index 0000000..3c97803
--- /dev/null
+++ b/src/sonar.rs
@@ -0,0 +1,29 @@
+use std::fs::File;
+use std::io;
+use std::io::prelude::*;
+
+use bounded_vec_deque::BoundedVecDeque;
+
+pub fn count_increases(filename: &str, window: usize) -> io::Result<i32> {
+    let f = File::open(filename)?;
+    let buf = io::BufReader::new(f);
+    let mut deque: BoundedVecDeque<i32> =
+        BoundedVecDeque::with_capacity(window, window);
+    let mut last = -1;
+    let mut count_incr = 0;
+    for line in buf.lines() {
+        if let Ok(l) = line {
+            if let Ok(value) = i32::from_str_radix(&l, 10) {
+                deque.push_back(value);
+            }
+            if deque.is_full() {
+                let sum = deque.iter().sum();
+                if last > -1 && sum > last {
+                    count_incr += 1;
+                }
+                last = sum;
+            }
+        }
+    }
+    Ok(count_incr)
+}