#include <bits/stdc++.h>
using namespace std;
signed main() {
int n,m; cin>>n>>m;
string s,t; cin>>s>>t;
int64_t dp[m+2][n+2];
for(int i = 0 ; i <= m ; i++) {
for(int j = 0 ; j <= n+1 ; j++) {
dp[i][j] = INT_MAX;
}
}
for(int i = 0 ; i <= n+1 ; i++) dp[0][i]=0;
for(int i = 0 ; i < m ; i++) {
for(int j = 1 ; j <= n ; j++) {
if(s[j-1] != t[i]) continue;
dp[i+1][j]=min(dp[i+1][j],min(dp[i][j-1],dp[i][j+1])+1);
for(int k = 1 ; k <= n ; k++) {
if(s[k-1] == t[i]) {
dp[i+1][k] = min(dp[i+1][k],dp[i+1][j] + abs(j-k));
}
}
}
}
int64_t mn = INT_MAX;
for(int i = 0 ; i <= n ; i++) {
mn=min(mn,dp[m][i]);
}
if (mn==INT_MAX){
cout<<-1<<endl;
}
else
cout << mn-1;
}
