#include <iostream>
#include <algorithm>

using namespace std;

int const MAX = 1100;
int const INF = 1<<29;

int N, M;
string S, T;

int dp[MAX][MAX];

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

int main() {

  cin >> N >> M >> S >> T;
  fill(dp[0], dp[0]+MAX*MAX, INF);

  S += '?', T += '?';

  dp[0][0] = 0;
  rep(i, N+1) rep(j, M+1) {
    if(S[i] == T[j]) {
      dp[i+1][j+1] = min(dp[i+1][j+1], dp[i][j]);
    }
    else {
      dp[i+1][j+1] = min(dp[i+1][j+1], dp[i][j] + 1);
      dp[i+1][j] = min(dp[i+1][j], dp[i][j] + 1);
      dp[i][j+1] = min(dp[i][j+1], dp[i][j] + 1);
    }
  }

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

  return 0;
}