#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cctype>
#include <cassert>
#include <climits>
#include <string>
#include <bitset>
#include <cfloat>
#include <unordered_set>
#include <iomanip>
//#pragma GCC optimize("Ofast")  //デバッグ時にoptimized-outされて邪魔だった
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int,int> > vpii;
typedef vector<vector<int> > vvi;
typedef vector<vector<char> > vvc;
typedef vector<vector<string> > vvs;
typedef vector<vector<ll> > vvll;
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define irep(it, stl) for(auto it = stl.begin(); it != stl.end(); it++)
#define drep(i,n) for(int i = (n) - 1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define mp(p,q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define floatprec(dig) fixed << setprecision(dig)
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define itn int;
#define invar(typ, var) typ var; cin >> var;
int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;} return 0;}
template <class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;} return 0;}
struct io{io(){ios::sync_with_stdio(false);cin.tie(0);}};
const int INF = INT_MAX;
const ll LLINF = 1LL<<60;
const ll MOD = 1000000007;
const double EPS = 1e-9;

int dp[1002][1002];

signed main(void) {
  cin.tie(0); ios::sync_with_stdio(false);
  
  invar(int, n); invar(int, m);
  invar(string, S); invar(string, T);
  
  rep(i, n + 1) rep(j, m + 1) dp[i][j] = INF / 2;
  dp[0][0] = 0;
  
  for(int i=-1; i<n; ++i) {
    for(int j=-1; j<m; ++j) {
      //-1からみる必要がある
      if(i==-1 && j==-1) continue;
      dp[i+1][j+1] = min(
        i >=0 && j >= 0 ? (S[i] == T[j] ? dp[i][j] : dp[i][j] + 1) : INF, //変更
        min(
          i >= 0 ? dp[i][j+1] + 1 : INF,  //追加
          j >= 0 ? dp[i+1][j] + 1 : INF //jは次に進むが，iは変わらない => 削除
        )
      );
    }
  }
  
  fin(dp[n][m]);
}