diff --git a/src/main.rs b/src/main.rs
index ad66668..1eaea06 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -30,7 +30,7 @@ fn main() -> Result<()> {
         }
         let mut prediction = 0;
         for seq in sequences.iter().rev() {
-            prediction += seq.last().unwrap();
+            prediction = seq.first().unwrap() - prediction;
         }
         println!("{prediction}");
         sum += prediction;