文字列処理の問題 `x='Department of Intelligent Systems Engineering'` `y` `y` `x` `x` `y` `x` `'NULL'` y'g': `'ent Systems Engineering'` `'ineering'`

x='Department of Intelligent Systems Engineering'
y = input(":")
for i in range(2):
try:
j = x.index(y)
x = x[j+len(y):]
print(x)
except ValueError:
print("NULL")
exit()