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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.io.*;
import java.util.*;

public class Main {

	final static long MOD = 1000000007L;
	public static String[] Ws = null;
	public static int wsIndx = 0;
	public static BufferedReader in = null;
	public static ArrayList<int[]> list = new ArrayList<>();
	public static void main(String[] args) throws Exception {


		int N = nextInt();
		int M = nextInt();
		String S = nextString();
		String T = nextString();
		int ans=(int)lcm((long)N,(long)M);

		int gcd=(int)gcd((long)N,(long)M);
		for(int i=0;i<gcd;i++){
			if(S.charAt((N/gcd)*i)!=T.charAt((M/gcd)*i)){
				ans=-1;
				break;
			}
		}

		System.out.println(ans);

	}

public static long gcd(long a, long b) {
	long x, y;
	if (a < b) {
		x = b;
		y = a;
	} else {
		x = a;
		y = b;
	}
	long r;
	while ((r = a % b) != 0) {
		a = b;
		b = r;
	}
	return b;
}

public static long lcm(long a, long b) {
	long x, y;

	return ((a/gcd(a,b))*b);
}


	public static String[] toStringArray(String s) {
		String[] tmp = new String[s.length()];
		char[] c = s.toCharArray();
		for (int i = 0; i < tmp.length; i++) {
			tmp[i] = String.valueOf(c[i]);
		}
		return tmp;
	}

	public static String concatStringArray(String[] s){
		StringBuffer sb = new StringBuffer();
		for(String x:s){
			sb.append(x);
		}
		return sb.toString();
	}

	public static void check() throws Exception{
		if(in == null){
			in = new BufferedReader(new InputStreamReader(System.in));
		}
		if(Ws==null || Ws.length<=wsIndx){
			Ws = in.readLine().split(" ");
			wsIndx=0;
		}
	}
	public static int nextInt()throws Exception{
		check();
		return Integer.parseInt(Ws[wsIndx++]);
	}

	public static long nextLong()throws Exception{
		check();
		return Long.parseLong(Ws[wsIndx++]);
	}

	public static String nextString()throws Exception{
		check();
		return Ws[wsIndx++];
	}

	public static int[] nextInts()throws Exception{
		check();
		int[] tmp = new int[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Integer.parseInt(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static long[] nextLongs()throws Exception{
		check();
		long[] tmp = new long[Ws.length];
		for(int i=0;i<tmp.length;i++){
			tmp[i]=Long.parseLong(Ws[i]);
		}
		wsIndx=Ws.length;
		return tmp;
	}

	public static String[] nextStrings()throws Exception{
		check();
		wsIndx=Ws.length;
		return Ws;
	}


}