Buggy python submission (verdict: Runtime Error):
import re
import sys
import math
import itertools
import bisect
from copy import copy
from collections import deque,Counter
from decimal import Decimal
import functools
def v(): return input()
def k(): return int(input())
def S(): return input().split()
def I(): return map(int,input().split())
def X(): return list(input())
def L(): return list(input().split())
def l(): return list(map(int,input().split()))
def lcm(a,b): return a*b//math.gcd(a,b)
sys.setrecursionlimit(10 ** 9)
mod = 10**9+7
cnt = 0
ans = 0
inf = float("inf")

n,m = I()
s = v()
t = v()
l = lcm(n,m)
g = gcd(n,m)

for i in range(g):
    if s[n//g*i] != t[m//g*i]:
        print(-1)
        sys.exit()

print(l)


Fixed submission:
import re
import sys
import math
import itertools
import bisect
from copy import copy
from collections import deque,Counter
from decimal import Decimal
import functools
def v(): return input()
def k(): return int(input())
def S(): return input().split()
def I(): return map(int,input().split())
def X(): return list(input())
def L(): return list(input().split())
def l(): return list(map(int,input().split()))
def lcm(a,b): return a*b//math.gcd(a,b)
sys.setrecursionlimit(10 ** 9)
mod = 10**9+7
cnt = 0
ans = 0
inf = float("inf")

n,m = I()
s = v()
t = v()
l = lcm(n,m)
g = math.gcd(n,m)

for i in range(g):
    if s[n//g*i] != t[m//g*i]:
        print(-1)
        sys.exit()

print(l)

Buggy python submission (verdict: Runtime Error):
import re
import sys
import math
import itertools
import bisect
from copy import copy
from collections import deque,Counter
from decimal import Decimal
import functools
def v(): return input()
def k(): return int(input())
def S(): return input().split()
def I(): return map(int,input().split())
def X(): return list(input())
def L(): return list(input().split())
def l(): return list(map(int,input().split()))
def lcm(a,b): return a*b//math.gcd(a,b)
sys.setrecursionlimit(10 ** 9)
mod = 10**9+7
cnt = 0
ans = 0
inf = float("inf")

n,m = I()
s = v()
t = v()
l = lcm(n,m)
x = l//n
y = l//m
g = lcm(x,y)
a = 1

while len(s)>= g and len(t)>= g:
    if s[a-1] != t[a-1]:
        print(-1)
        sys.exit()
    a += g

print(l)


Fixed submission:
import re
import sys
import math
import itertools
import bisect
from copy import copy
from collections import deque,Counter
from decimal import Decimal
import functools
def v(): return input()
def k(): return int(input())
def S(): return input().split()
def I(): return map(int,input().split())
def X(): return list(input())
def L(): return list(input().split())
def l(): return list(map(int,input().split()))
def lcm(a,b): return a*b//math.gcd(a,b)
sys.setrecursionlimit(10 ** 9)
mod = 10**9+7
cnt = 0
ans = 0
inf = float("inf")

n,m = I()
s = v()
t = v()
l = lcm(n,m)
g = math.gcd(n,m)

for i in range(g):
    if s[n//g*i] != t[m//g*i]:
        print(-1)
        sys.exit()

print(l)

Buggy python submission (verdict: Runtime Error):
import re
import sys
import math
import itertools
import bisect
from copy import copy
from collections import deque,Counter
from decimal import Decimal
import functools
def v(): return input()
def k(): return int(input())
def S(): return input().split()
def I(): return map(int,input().split())
def X(): return list(input())
def L(): return list(input().split())
def l(): return list(map(int,input().split()))
def lcm(a,b): return a*b//math.gcd(a,b)
sys.setrecursionlimit(10 ** 9)
mod = 10**9+7
cnt = 0
ans = 0
inf = float("inf")

n,m = I()
s = v()
t = v()
l = lcm(n,m)
x = l//n
y = l//m
p = [-1]*l
k = 0
b = 0
for i in range(0,n,x):
    p[i]=s[k]
    k += 1

for j in range(0,m,y):
    if p[j] != -1 and p[j] != t[b]:
        print(-1)
        sys.exit()
    else:
        p[j]=t[b]
    b += 1

print(l)


Fixed submission:
import re
import sys
import math
import itertools
import bisect
from copy import copy
from collections import deque,Counter
from decimal import Decimal
import functools
def v(): return input()
def k(): return int(input())
def S(): return input().split()
def I(): return map(int,input().split())
def X(): return list(input())
def L(): return list(input().split())
def l(): return list(map(int,input().split()))
def lcm(a,b): return a*b//math.gcd(a,b)
sys.setrecursionlimit(10 ** 9)
mod = 10**9+7
cnt = 0
ans = 0
inf = float("inf")

n,m = I()
s = v()
t = v()
l = lcm(n,m)
g = math.gcd(n,m)

for i in range(g):
    if s[n//g*i] != t[m//g*i]:
        print(-1)
        sys.exit()

print(l)