#include <bits/stdc++.h>
using namespace std;
int n, m, mi = INT_MAX;
char a[305], b[305];
void DFS(int i, int deep, int cost) {
	if (deep == m + 1) {
		mi = min(mi, deep);
	}
	if (a[i - 1] == b[deep + 1]) {
		DFS(i - 1, deep + 1, cost + 1);
	}
	else if (a[i + 1] == b[deep + 1]) {
		DFS(i + 1, deep + 1, cost + 1);
	}
	else{
		for (int j = 0; j < n; j++) {
			if ((a[j - 1] == b[deep + 1] || a[j + 1] == b[deep + 1]) && j != i) {
				DFS(j, deep + 1, cost + abs(i - j) + 1);
			}
		}
	}
	
}
int main() {
	cin >> n >> m;
	cin >> a >> b;
	for (int i = 0; i < n; i++) {
		if (a[i] == b[0]) {
			DFS(i, 0, 0);
		}
	}
	if (mi == INT_MAX) {
		cout << -1;
	} else {
		cout << mi - 1;
	}
	return 0;
}