#include <bits/stdc++.h>
#include <atcoder/all>

using namespace std;
using namespace atcoder;
// @formatter:off
using ll = long long;
using P = pair<ll, ll>;
using Graph = vector<vector<ll>>;
#define rep(i, n) for(ll i=0;i<(ll)(n);i++)
#define rep2(i, m, n) for(ll i=m;i<(ll)(n);i++)
#define rrep(i, n, m) for(ll i=n;i>=(ll)(m);i--)
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
const int ddx[8] = {0, 1, 1, 1, 0, -1, -1, -1};
const int ddy[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll MOD = 1000000007;
const ll INF = 1000000000000000000L;
template<typename T> bool chmax(T &a, const T &b) {if (a < b){a = b;return true;}else{return false;}}
template<typename T> bool chmin(T &a, const T &b) {if (a > b){a = b;return true;}else{ return false;}}

#ifdef __DEBUG
/**
 * For DEBUG
 * https://github.com/ta7uw/cpp-pyprint
 */
#include "cpp-pyprint/pyprint.h"

#else
#define print(...)
#endif
// @formatter:on

void solve() {
    ll N, M;
    string S, T;
    cin >> N >> M >> S >> T;
    vector<vector<ll>> dp(N + 1, vector<ll>(M + 1, INF));
    dp[0][0] = 0;
    rep(i, N + 1) {
        rep(j, M + 1) {
            if (i == N) {
                chmin(dp[i][j + 1], dp[i][j] + 1);
                continue;
            }
            if (j == M) {
                chmin(dp[i + 1][j], dp[i][j] + 1);
                continue;
            }
            if (S[i] == T[j]) {
                chmin(dp[i + 1][j + 1], dp[i][j]);
            }
            chmin(dp[i + 1][j], dp[i][j] + 1);
            chmin(dp[i][j + 1], dp[i][j] + 1);
            chmin(dp[i + 1][j + 1], dp[i][j] + 1);
        }
    }
    cout << dp[N][M] << '\n';
}

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(15);
    solve();
    return 0;
}