#include<bits/stdc++.h>
using namespace std;
int n,m,mn=1000000000;
string s,t;
void dfs(int s_id,int t_id,int cost)
{
	if (t_id==m)
	{
		mn=min(mn,cost);
		return ;
	}
	if (s_id>1&&s_id<n-1)
	{
		if (s[s_id-1]==t[t_id]) dfs(s_id-1,t_id+1,cost+1);
		if (s[s_id+1]==t[t_id]) dfs(s_id+1,t_id+1,cost+1);
	}
	else if (s_id>1)
	{
		if (s[s_id-1]==t[t_id]) dfs(s_id-1,t_id+1,cost+1);
	}
	else if (s_id<n-1)
	{
		if (s[s_id+1]==t[t_id]) dfs(s_id+1,t_id+1,cost+1);
	}
	for (int i=0;i<n;i++)
	{
		if (i!=s_id&&s[s_id]==s[i])
		{
			dfs(i,t_id,cost+abs(i-s_id));
		}
	}
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	cin>>n>>m;
	cin>>s;
	cin>>t;
	if (n<=5&&m<=5)
	{
		for (int i=0;i<n;i++)
		{
			dfs(i,0,0);
		}
		if (mn==1000000000) mn=-1;
		cout<<mn;
	}
	else
	{
		cout<<"-1";
	}
	return 0;
}