Help me in solving TRISWP problem

help
,
1

My issue

Why is this giving runtime error??
t = int(input())
for _ in range(t):
n = int(input())
s = input()

possible = set()
for i in range(n - 2):
    s1 = s[i + 1] + s[i + 2] + s[i]
    s1 = s[:i] + s1 + s[i+3:]
    possible.add(s1)
    
print(len(possible))

My code

t = int(input())
for _ in range(t):
    n = int(input())
    s = input()
    
    possible = set()
    for i in range(n - 2):
        s1 = s[i + 1] + s[i + 2] + s[i]
        s1 = s[:i] + s1 + s[i+3:]
        possible.add(s1)
        
    print(len(possible))

Problem Link: Triangular Swaps Practice Coding Problem - CodeChef