diff --git a/lab4/src/Lib.hs b/lab4/src/Lib.hs
index 7c78342..5c91057 100644
--- a/lab4/src/Lib.hs
+++ b/lab4/src/Lib.hs
@@ -4,7 +4,7 @@ module Lib
     ) where
 
 isCongruent :: Int -> Int -> Int -> Bool
-isCongruent a b d = a `mod` d + 1 == b `mod` d
+isCongruent a b d = a `mod` d == b `mod` d
 
 
 filterByPredicate :: (a -> Bool) -> [a] -> [a]