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: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
using ll=long long;

int gcd(int a,int b){return a%b?gcd(b,a%b):b;}
int lcm(int c,int d){return c*d/gcd(c,d);}
int main(){
    int n,m;
    cin>>n>>m;
    string s,t;
    cin>>s>>t;
    int ans=lcm(n,m);
    if(s.at(0)!=t.at(0)){cout<<-1<<endl;}
    else if(n==m){
        if(s==t)cout<<n<<endl;
        else cout<<-1<<endl;
     }
    else{
        bool flag=true;
        map<int,char> mp;
        for(int i=0;i<n;i++){
           int nown=ans/n*i;
            mp[nown]=s.at(i);
        }
        for(int i=0;i<m;i++){
            int nowm=ans/m*i;
            if(mp[nowm]!=0) if(mp[nowm]!=t.at(i)){flag=false;break;}
        }
        if(flag)cout<<ans<<endl;
        else cout<<-1<<endl;
    }
}