/* ---------- STL Libraries ---------- */
// IO library
#include <cstdio>
#include <fstream>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm library
#include <algorithm>
#include <cmath>
#include <numeric>
#include <random>

// container library
#include <array>
#include <bitset>
#include <deque>
#include <map>
#include <unordered_map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>

/* ---------- Namespace ---------- */
using namespace std;

/* ---------- Type ---------- */
using ll = long long;
#define int ll
#define P pair<ll, ll>

/* ---------- Constants  */
const double PI = 3.141592653589793238462643383279;
const ll MOD = 1e9 + 7;
const int INF = 1LL << 55;

/* v-v-v-v-v-v-v-v-v Main Part v-v-v-v-v-v-v-v-v */
signed main() {
    int N, M;
    string s, t;
    cin >> N >> M >> s >> t;

    int dp[N+1][M+1];
    fill(dp[0], dp[N+1], INF);
    dp[0][0] = 0;
    for (int i = 1; i <= N; i++) dp[i][0] = i;
    for (int j = 1; j <= M; j++) dp[0][j] = j;

    for (int i = 1; i <= N; i++) {
        for (int j = 1; j <= M; j++) {
            dp[i][j] = min(dp[i-1][j] + 1, dp[i][j-1] + 1);
            if (s[i-1] == t[j-1]) {
                dp[i][j] = min(dp[i][j], dp[i-1][j-1]);
            } else {
                dp[i][j] = min(dp[i][j], dp[i-1][j-1] + 1);
            }
        }
    }

    cout << dp[N][M] << endl;

    return 0;
}