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 Python (3.4.3) (judge verdict: Time Limit Exceeded)

N, M = [int(x) for x in input().split(" ")]
S = input()
T = input()

N = len(S)
M = len(T)


def gcd(a, b):
    if (a < b):
        return gcd(b, a)
    if a % b == 0:
        return b
    else:
        return gcd(b, a % b)


def maxkobai(a, b):
    return a * b // gcd(a, b)


#print(gcd(N, M))
#print(maxkobai(N, M))


L = maxkobai(N, M)
ret = L
x = ['-' for i in range(L+1)]

for n in range(0, N):
    x[n * (L//N) + 1] = S[n]

# print(x)

for m in range(0, M):
    idx = m * (L // M) + 1
    if x[idx] != '-':
        if (x[idx] != T[m]):
            ret = -1
            break

print(ret)