diff --git a/tools/int_seq.py b/tools/int_seq.py
index 3e00b20..aedcd07 100644
--- a/tools/int_seq.py
+++ b/tools/int_seq.py
@@ -10,7 +10,6 @@ def factorial(n: int) -> int:
     return math.factorial(n)
 
 
-@cache
 def fibonacci(n: int) -> int:
     """
     F(n) = F(n-1) + F(n-2) with F(0) = 0 and F(1) = 1
@@ -19,7 +18,11 @@ def fibonacci(n: int) -> int:
     if n < 2:
         return n
 
-    return fibonacci(n - 1) + fibonacci(n - 2)
+    l, r = 1, 1
+    for _ in range(n - 2):
+        l, r = l + r, l
+
+    return l
 
 
 def triangular(n: int) -> int: