#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)n;++i)
#define each(a, b) for(auto (a): (b))
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
#define pb push_back
#define show(x) cout <<#x<<" = "<<(x)<<endl
#define spair(p) cout <<#p<<": "<<p.fi<<" "<<p.se<<endl
#define svec(v) cout<<#v<<":";rep(kbrni,v.size())cout<<" "<<v[kbrni];cout<<endl
#define sset(s) cout<<#s<<":";each(kbrni,s)cout <<" "<<kbrni;cout<<endl

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 1002;

int dp[MAX_N][MAX_N];

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n,m;
    cin >> n >> m;
    string s,t;
    cin >> s >> t;
    rep(i,n+1){
        rep(j,m+1){
            dp[i][j] = INF;
        }
    }
    rep(i,n+1){
        dp[i][0] = i;
    }
    rep(j,m+1){
        dp[0][j] = j;
    }
    rep(i,n){
        rep(j,m){
            if(s[i] == t[j]){
                dp[i+1][j+1] = min(dp[i+1][j+1],dp[i][j]);
            }
            dp[i+1][j+1] = min(dp[i+1][j+1],dp[i+1][j]+1);
            dp[i+1][j+1] = min(dp[i+1][j+1],dp[i][j+1]+1);
            dp[i+1][j+1] = min(dp[i+1][j+1],dp[i][j]+1);
        }
    }
    cout << dp[n][m] << endl;
    return 0;
}