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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
using namespace std;
long gcd(long a,long b){
    if(a < b)swap(a,b);
    if(a%b == 0)return b;
    else return gcd(b,a%b);
}

long lcm(long a,long b){
    return a*b/gcd(a,b);
}

int main(){
    long n,m;
    cin >> n >> m;
    string s,t;
    cin >> s >> t;
    long lcmm = lcm(n,m);
    long gcdd = gcd(n,m);
    bool chk = true;
    long a = lcmm/n;
    long b = lcmm/m;
    
    for(int i=0;i<gcdd;i++){
        if(s[i*b] != t[i*a])chk = false;
    }

    if(!chk)lcmm = -1;
    cout << lcmm << endl;
    
}