#include <iostream>
#include <algorithm>
using namespace std;
using i64 = long long;

class range {private: struct I{int x;int operator*(){return x;}bool operator!=(I& lhs){return x<lhs.x;}void operator++(){++x;}};I i,n;
public:range(int n):i({0}),n({n}){}range(int i,int n):i({i}),n({n}){}I& begin(){return i;}I& end(){return n;}};

const int inf = 19921223;

int main(void) {
  int n, m; scanf("%d%d", &n, &m);
  string s, t; cin >> s >> t;
  vector<vector<int>> dp(n+1, vector<int>(m+1, inf));
  dp[0][0] = 0;
  for(int i : range(n+1)) {
    for(int j : range(m+1)) {
      if(i < n && j < m) { dp[i+1][j+1] = min(dp[i+1][j+1], dp[i][j] + (s[i]!=t[j])); }
      if(i < n) { dp[i+1][j] = min(dp[i+1][j], dp[i][j] + 1); }
      if(j < m) { dp[i][j+1] = min(dp[i][j+1], dp[i][j] + 1); }
    }
  }
  int res = dp[n][m];
  printf("%d\n", res);
  return 0;
}