#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000001


int main(){
	int n,m;
	cin>>n>>m;
	string s,t;
	cin>>s>>t;
	
	vector dp(n+1,vector<int>(m+1,Inf));
	dp[0][0] = 0;
	
	rep(i,n+1){
		rep(j,m+1){
			if(i!=n)dp[i+1][j] = min(dp[i+1][j],dp[i][j]+1);
			if(j!=m)dp[i][j+1] = min(dp[i][j+1],dp[i][j]+1);
			if(i!=n&&j!=m){
				int cost = 0;
				if(s[i]!=t[j])cost = 1;
				dp[i+1][j+1] = min(dp[i+1][j+1], dp[i][j]+cost);
			}
		}
	}
	cout<<dp[n][m]<<endl;
	
	return 0;
}