diff --git a/inputs/4.small.txt b/inputs/4.small.txt
new file mode 100644
index 0000000..9f9e9cf
--- /dev/null
+++ b/inputs/4.small.txt
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diff --git a/inputs/4.txt b/inputs/4.txt
new file mode 100644
index 0000000..b52da37
--- /dev/null
+++ b/inputs/4.txt
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diff --git a/src/main.rs b/src/main.rs
index 98aed56..bdeff1e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,6 +1,6 @@
-use std::cmp::Ordering;
 use std::collections::HashSet;
 use std::fs;
+use std::{cmp::Ordering, ops::RangeInclusive as Range};
 
 use anyhow::Error;
 use chrono::{Datelike, Local};
@@ -16,6 +16,7 @@ fn main() -> Result<(), Error> {
     let small = if small { ".small" } else { "" };
     let path = format!("inputs/{day}{small}.txt");
     let input = fs::read_to_string(path)?;
+    println!("running day {day} part {part}");
     let result = SOLNS[day as usize - 1][part as usize - 1](input);
     println!("{result}");
     Ok(())
@@ -23,7 +24,7 @@ fn main() -> Result<(), Error> {
 
 type Part = fn(String) -> u64;
 type Day = [Part; 2];
-const DAYS: usize = 3;
+const DAYS: usize = 4;
 const SOLNS: [Day; DAYS] = [
     [
         // day 1 part 1
@@ -114,8 +115,62 @@ const SOLNS: [Day; DAYS] = [
                 .sum()
         },
     ],
+    [
+        // day 4 part 1
+        |input| {
+            make_ranges(input)
+                .iter()
+                .map(|(first, second)| {
+                    range_contains(first, second) || range_contains(second, first)
+                })
+                .map(|b| if b { 1 } else { 0 })
+                .sum()
+        },
+        // day 4 part 2
+        |input| {
+            make_ranges(input)
+                .iter()
+                .map(|(first, second)| {
+                    range_overlaps(first, second) || range_overlaps(second, first)
+                })
+                .map(|b| if b { 1 } else { 0 })
+                .sum()
+        },
+    ],
 ];
 
+fn make_ranges(input: String) -> Vec<(Range<u64>, Range<u64>)> {
+    input
+        .lines()
+        .map(|line| {
+            line.split(',')
+                .map(|range| {
+                    range
+                        .split('-')
+                        .map(|num| num.parse::<u64>().expect("bad num :/"))
+                })
+                .map(|mut nums| {
+                    let lo = nums.next().expect("nolo :/");
+                    let hi = nums.next().expect("nohi :/");
+                    lo..=hi
+                })
+        })
+        .map(|mut ranges| {
+            let f = ranges.next().unwrap();
+            let s = ranges.next().unwrap();
+            (f, s)
+        })
+        .collect()
+}
+
+fn range_contains(r1: &Range<u64>, r2: &Range<u64>) -> bool {
+    r1.start() <= r2.start() && r1.end() >= r2.end()
+}
+
+fn range_overlaps(r1: &Range<u64>, r2: &Range<u64>) -> bool {
+    r1.contains(r2.start())
+}
+
 #[derive(Copy, Clone, PartialEq, Eq)]
 enum RPS {
     Rock,