#include <bits/stdc++.h>
#define F first
#define S second
#define pb push_back
#define ppb pop_back
#define ep insert
#define endl '\n'
#define elif else if
#define pow pwr
#define sqrt sqrtt
#define int long long
typedef unsigned long long ull;
using namespace std;
const int N=305;
int dp[N][N],n,m;
char a[N],b[N];
bool vis[N][N];
vector<int> adj[30];
int rec(int i,int j){
//cout<<i<<' '<<j<<endl;
if (j==m) return 0;
if (vis[i][j]) return dp[i][j];
vis[i][j]=true;
dp[i][j]=INT_MAX;
if (i>1){
if (a[i-1]==b[j+1]) dp[i][j]=min(dp[i][j],rec(i-1,j+1)+1);
}
if (i<n){
if (a[i+1]==b[j+1]) dp[i][j]=min(dp[i][j],rec(i+1,j+1)+1);
}
for (auto u:adj[a[i]-'a']) dp[i][j]=min(dp[i][j],rec(u,j)+abs(u-i));
return dp[i][j];
}
int32_t main(){
ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
cin>>n>>m;
for (int i=1;i<=n;i++){
cin>>a[i];
adj[a[i]-'a'].pb(i);
}
for (int j=1;j<=m;j++) cin>>b[j];
int ans=INT_MAX;
for (int i=1;i<=n;i++) ans=min(ans,rec(i,0));
if (ans>=INT_MAX) cout<<-1<<endl;
else cout<<ans-1<<endl;
return 0;
}
