diff --git a/introduction/serie_2.py b/introduction/serie_2.py
index e6811ae..c86393f 100644
--- a/introduction/serie_2.py
+++ b/introduction/serie_2.py
@@ -4,32 +4,46 @@ import numpy as np
 # %%
 print("Aufgabe 4")
 
-def fixpunkt_iteration(f, x, tol=1e-7):
+def fixpunkt_iteration(f, x=1.0, tol=1e-7, N=1000):
     x_new = f(x)
     i = 0
 
     while(np.abs(x_new-x) > tol):
+        if i > N:
+            raise RuntimeError("Keine Konvergenz erreicht")
+
         x = x_new
         x_new = f(x)
         i += 1
     return [x_new, i]
 
-x0 = 1.0
-
-f = lambda x: 1-(1/5)*x
-fixpunkt_a, iterationen_a = fixpunkt_iteration(f, x0)
-
-f = np.cos
-fixpunkt_b, iterationen_b = fixpunkt_iteration(f, x0)
-
-f = lambda x: np.e**-x
-fixpunkt_c, iterationen_c = fixpunkt_iteration(f, x0)
-
 # Ausgabe
 print("----------------------------------------------------------------------")
 print(__file__)
 print("----------------------------------------------------------------------")
-print(f"a) f(x) = 1-(1/5)*x\nFixpunkt: {fixpunkt_a}\nIterationen: {iterationen_a}\n")
-print(f"b) f(x) = cos(x)\nFixpunkt: {fixpunkt_b}\nIterationen: {iterationen_b}\n")
-print(f"c) f(x) = e⁻x\nFixpunkt: {fixpunkt_c}\nIterationen: {iterationen_c}\n")
+
+f = lambda x: 1-(1/5)*x
+try:
+    fixpunkt_a, iterationen_a = fixpunkt_iteration(f)
+except RuntimeError as error:
+    print(f"a) f(x) = 1-(1/5)*x\n{error}")
+else:
+    print(f"a) f(x) = 1-(1/5)*x\nFixpunkt: {fixpunkt_a}\nIterationen: {iterationen_a}\n")
+
+f = np.cos
+try:
+    fixpunkt_b, iterationen_b = fixpunkt_iteration(f)
+except RuntimeError as error:
+    print(f"b) f(x) = cos(x)\n{error}")
+else:
+    print(f"b) f(x) = cos(x)\nFixpunkt: {fixpunkt_b}\nIterationen: {iterationen_b}\n")
+
+f = lambda x: np.e**-x
+try:
+    fixpunkt_c, iterationen_c = fixpunkt_iteration(f)
+except RuntimeError as error:
+    print(f"c) f(x) = e⁻x\n{error}")
+else:
+    print(f"c) f(x) = e⁻x\nFixpunkt: {fixpunkt_c}\nIterationen: {iterationen_c}\n")
+
 print("----------------------------------------------------------------------")