#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<map>
#include<string>
#include<algorithm>
#include<functional>
using namespace std;
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define INF 1<<30
#define MP make_pair
#define mp make_pair
#define pb push_back
#define PB push_back
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define ll long long
#define ull unsigned long long

int main(){
	int n,m;
	string s,t;
	cin>>n>>m;
	cin>>s>>t;
	int dp[n+1][m+1];fill((int*)dp,(int*)dp+(n+1)*(m+1),INF);
	dp[0][0]=0;
	REP(i,n+1) dp[i][0]=i;
	REP(i,m+1) dp[0][i]=i;
	FOR(i,1,n+1){
		FOR(j,1,m+1){
				if(s[i-1]==t[j-1]) dp[i][j]=min(dp[i][j],dp[i-1][j-1]);
				if(s[i-1]!=t[j-1]) dp[i][j]=min(dp[i][j],dp[i-1][j-1]+1);
				dp[i][j] = min(dp[i][j],dp[i-1][j]+1);
				dp[i][j] = min(dp[i][j],dp[i][j-1]+1);
		}
	}
	cout<<dp[n][m]<<endl;
	return 0;
}