Buggy python submission (verdict: Time Limit Exceeded):
from fractions import gcd

n, m = [int(i) for i in input().split()]
S = input()
T = input()

g = n * m // gcd(n, m)

try:

    L = ['' for i in range(g)]

except:
    print(-1)
    exit()

if S[0] != T[0]:
    print(-1)
    exit()

for i, s in zip(range(0, g, g//n), S):
    L[i] = s

for i, t in zip(range(0, g, g//m), T):
    L[i] = t
    
A = []
B = []

for i in range(0, g, g//n):
    A.append(L[i])

for i in range(0, g, g//m):
    B.append(L[i])

if ''.join(A) == S and ''.join(B) == T:
    print(g)
else:
    print(-1)



Fixed submission:
from fractions import gcd

n, m = [int(i) for i in input().split()]
S = input()
T = input()

g = n * m // gcd(n, m)

SA = set()
SB = set()

for i in range(0, g, g//n):
    SA.add(i)

for i in range(0, g, g//m):
    SB.add(i)

SC = SA & SB

for s in SC:
    if S[s//(g//n)] != T[s//(g//m)]:
        print(-1)
        exit()

print(g)

Buggy python submission (verdict: Runtime Error):
from fractions import gcd

n, m = [int(i) for i in input().split()]
S = input()
T = input()

g = n * m // gcd(n, m)

try:

    L = [''] * g

except:
    print(-1)

if S[0] != T[0]:
    print(-1)
    exit()

for i, s in zip(range(0, g, g//n), S):
    L[i] = s

for i, t in zip(range(0, g, g//m), T):
    L[i] = t
    
A = []
B = []

for i in range(0, g, g//n):
    A.append(L[i])

for i in range(0, g, g//m):
    B.append(L[i])

if ''.join(A) == S and ''.join(B) == T:
    print(g)
else:
    print(-1)

Fixed submission:
from fractions import gcd

n, m = [int(i) for i in input().split()]
S = input()
T = input()

g = n * m // gcd(n, m)

SA = set()
SB = set()

for i in range(0, g, g//n):
    SA.add(i)

for i in range(0, g, g//m):
    SB.add(i)

SC = SA & SB

for s in SC:
    if S[s//(g//n)] != T[s//(g//m)]:
        print(-1)
        exit()

print(g)

Buggy python submission (verdict: Runtime Error):
from fractions import gcd

n, m = [int(i) for i in input().split()]
S = input()
T = input()

g = n * m // gcd(n, m)

L = [''] * g
if S[0] != T[0]:
    print(-1)
    exit()

try:
    for i, s in zip(range(0, g, g//n), S):
        L[i] = s

    for i, t in zip(range(0, g, g//m), T):
        L[i] = t
        
    A = []
    B = []

    for i in range(0, g, g//n):
        A.append(L[i])

    for i in range(0, g, g//m):
        B.append(L[i])

    if ''.join(A) == S and ''.join(B) == T:
        print(g)
    else:
        print(-1)

except:
    print(-1)

Fixed submission:
from fractions import gcd

n, m = [int(i) for i in input().split()]
S = input()
T = input()

g = n * m // gcd(n, m)

SA = set()
SB = set()

for i in range(0, g, g//n):
    SA.add(i)

for i in range(0, g, g//m):
    SB.add(i)

SC = SA & SB

for s in SC:
    if S[s//(g//n)] != T[s//(g//m)]:
        print(-1)
        exit()

print(g)

Buggy python submission (verdict: Runtime Error):
from fractions import gcd

n, m = [int(i) for i in input().split()]
S = input()
T = input()

g = n * m // gcd(n, m)

L = [''] * g
if S[0] != T[0]:
    print(-1)
    exit()

for i, s in zip(range(0, g, g//n), S):
    L[i] = s

for i, t in zip(range(0, g, g//m), T):
    L[i] = t
    
A = []
B = []

for i in range(0, g, g//n):
    A.append(L[i])

for i in range(0, g, g//m):
    B.append(L[i])

if ''.join(A) == S and ''.join(B) == T:
    print(g)
else:
    print(-1)

Fixed submission:
from fractions import gcd

n, m = [int(i) for i in input().split()]
S = input()
T = input()

g = n * m // gcd(n, m)

SA = set()
SB = set()

for i in range(0, g, g//n):
    SA.add(i)

for i in range(0, g, g//m):
    SB.add(i)

SC = SA & SB

for s in SC:
    if S[s//(g//n)] != T[s//(g//m)]:
        print(-1)
        exit()

print(g)