Problem:
Score : 300 points

Problem Statement

You are given a string S of length N and another string T of length M.
These strings consist of lowercase English letters.

A string X is called a good string when the following conditions are all met:

Let L be the length of X. L is divisible by both N and M.

Concatenating the 1-st, (\frac{L}{N}+1)-th, (2 \times \frac{L}{N}+1)-th, ..., ((N-1)\times\frac{L}{N}+1)-th characters of X, without changing the order, results in S.

Concatenating the 1-st, (\frac{L}{M}+1)-th, (2 \times \frac{L}{M}+1)-th, ..., ((M-1)\times\frac{L}{M}+1)-th characters of X, without changing the order, results in T.

Determine if there exists a good string. If it exists, find the length of the shortest such string.

Constraints

1 \leq N,M \leq 10^5

S and T consist of lowercase English letters.

|S|=N

|T|=M

Input

Input is given from Standard Input in the following format:

N M
S
T

Output

If a good string does not exist, print -1; if it exists, print the length of the shortest such string.

Sample Input 1

3 2
acp
ae

Sample Output 1

6

For example, the string accept is a good string.
There is no good string shorter than this, so the answer is 6.

Sample Input 2

6 3
abcdef
abc

Sample Output 2

-1

Sample Input 3

15 9
dnsusrayukuaiia
dujrunuma

Sample Output 3

45

Solution in PyPy3 (2.4.0) (judge verdict: Runtime Error)

def gcd(a,b): return a if b==0 else gcd(b,a%b)
def lcm(a,b): return a*b//gcd(a,b)
n,m=map(int,input().split())
s=input()
t=input()
n,m=max(n,m),min(n,m)
l=lcm(n,m)
d=[set() for i in range(l)]
f=l
for i in range(max(n,m)):
    o=i*(l//n)
    p=i*(l//m)
    if i<n: d[o].add(s[i])
    if i<m: d[p].add(t[i])
    if i<n and len(d[o])==2: f=-1
    if i<m and len(d[p])==2: f=-1
print(f)