I am getting runtime error in some of the test cases. Help me solving the issue

Question

https://www.hackerrank.com/contests/projecteuler/challenges/euler230/problem

Answer 1

q=int(input())
for i in range(0,q):
A,B,n=input().split()
A,B,n=str(A),str(B),int(n)
while len(B)<n:
A+=B
B+=A
print((A)[n-1] if len(A)>n else (B)[n-1])

Answer 2

The way you are doing is very naive .

https://www.sololearn.com/post/431255/?ref=app
See codes by michal and bobby.
The problem arises when the size of string is too large.
Here's an hint:
F[n] = F[n-1]+ F[N-2]
Also see bobby's explanation there.