#include <bits/stdc++.h>
#define REP(i,n,N) for(int i=n;i<(int)N;i++)
#define p(S) cout<<(S)<<endl
using namespace std;

int dp[1001][1001];
int main(){
	int n,m;
	cin>>n>>m;
	string s,t;
	cin>>s>>t;
	REP(i,0,n+1) dp[i][0]=i;
	REP(i,0,m+1) dp[0][i]=i;
	REP(i,0,n){
		REP(j,0,m){
			dp[i+1][j+1]=min(dp[i+1][j],dp[i][j+1])+1;
			dp[i+1][j+1]=min(dp[i+1][j+1],dp[i][j]+(s[i]!=t[j]));
		}
	}
	p(dp[n][m]);
	return 0;
}