#include <iostream>
#include <vector>
#include <string>

template <class T>
std::vector<T> vec(int len, T elem) { return std::vector<T>(len, elem); }

constexpr int INF = 1 << 30;

void solve() {
    int n, m;
    std::string s, t;
    std::cin >> n >> m >> s >> t;

    auto dp = vec(n + 1, vec(m + 1, INF));
    for (int i = 0; i <= n; ++i) {
        for (int j = 0; j <= m; ++j) {
            if (i == 0 || j == 0) dp[i][j] = i + j;

            if (i + 1 <= n) dp[i + 1][j] = std::min(dp[i + 1][j], dp[i][j] + 1);
            if (j + 1 <= m) dp[i][j + 1] = std::min(dp[i][j + 1], dp[i][j] + 1);
            if (i + 1 <= n && j + 1 <= m) {
                dp[i + 1][j + 1] = std::min(dp[i + 1][j + 1],
                                            dp[i][j] + (s[i] != t[j]));
            }
        }
    }

    std::cout << dp[n][m] << "\n";
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}