diff --git a/04/.gitignore b/04/.gitignore
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@@ -0,0 +1 @@
+day04
diff --git a/04/README.md b/04/README.md
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+# [Day 4](https://adventofcode.com/2023/day/4) 
+:gift::gift::gift::gift:
+
+Today's language: **Rust**
+
+```shell
+rustc day04.rs
+./day04
+```
diff --git a/04/day04.rs b/04/day04.rs
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+++ b/04/day04.rs
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+use std::io::{self, BufRead};
+
+fn split_into_numbers(x: &str) -> impl Iterator<Item = i32> + '_ {
+    return x.split(' ').filter(|&n| {n != "" && n != " "}).map(|n| n.parse::<i32>().unwrap());
+}
+
+fn main() {
+    let input = "input.txt";
+    let lines = read_lines(&input);
+    let n_cards: usize = read_lines(&input).count();
+    let mut cards: Vec<u32> = vec![1; n_cards];
+    let mut sum_points: u32 = 0;
+    // number of copies per card
+    for (i, line) in lines.enumerate() {
+        let mut points: u32 = 0;
+        let mut n_matches: usize = 0;
+        let Ok(card) = line else { panic!("Line not ok"); };
+        let Some(colon) = card.find(':') else { panic!("Could not find ':'"); };
+        let Some(pipe) = card.find('|') else { panic!("Could not find '|'"); };
+        // let split_into_numbers = |x: &str| { return x.split(' ').filter(|&n| {n != "" && n != " "}).map(|n| n.parse::<i32>().unwrap()); };
+        let winning_numbers: Vec<i32> = split_into_numbers(&card[colon+2..pipe-1]).collect();
+        for number in split_into_numbers(&card[pipe+2..]) {
+            if winning_numbers.contains(&number) {
+                // task 1
+                if points == 0 { points = 1; }
+                else { points <<= 1; }
+                // task 2
+                if points == 0 { points = 1; }
+                n_matches += 1;
+            }
+        }
+        // task 1
+        sum_points += points;
+        // task 2: add #copies(card i) to the next n_matches cards
+        for j in i+1..i+1+n_matches {
+            cards[j] += cards[i];
+        }
+    }
+    println!("Total points: {}", sum_points);
+    println!("Total number of cards: {}", cards.iter().sum::<u32>());
+}
+
+fn read_lines<P>(filename: P) -> io::Lines<io::BufReader<std::fs::File>>
+where P: AsRef<std::path::Path>, {
+    return match std::fs::File::open(filename) {
+        Err(why) => panic!("Could not open file. {}", why),
+        Ok(file) => std::io::BufReader::new(file).lines()
+    };
+}