#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
using namespace std;

#define REP(i,s,e) for (i = s; i <= e; i++)
#define rep(i,n) REP (i,0,(int)(n)-1)
#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP (i,(int)(n)-1,0)
#define INF (int)1e8
#define MOD (int)1e9+7

int dp[1001][1001];

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