#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair< int, int > pii;
typedef vector< int > vi;
typedef vector< vi > vvi;
typedef vector< ll > vl;
typedef vector< vl > vvl;
typedef vector< pii > vp;
typedef vector< vp > vvp;
typedef vector< string > vs;
typedef vector< double > vd;
typedef vector< vd > vvd;

template< class T1, class T2 >
int upmin( T1 &x, T2 v ){
  if( x > v ){
    x = v;
    return 1;
  }
  return 0;
}

template< class T1, class T2 >
int upmax( T1 &x, T2 v ){
  if( x < v ){
    x = v;
    return 1;
  }
  return 0;
}

const int INF = 0x3f3f3f3f;

int N, M;
string S;
string T;

void init(){
  cin >> N >> M;
  cin >> S;
  cin >> T;
}

int dp[ 1000 + 1 ][ 1000 + 1 ];

void preprocess(){
  memset( dp, INF, sizeof( dp ) );
  dp[ 0 ][ 0 ] = 0;
  for( int i = 0; i <= N; ++i )
    for( int j = 0; j <= M; ++j )
      if( dp[ i ][ j ] < INF ){
        if( i < N and j < M and S[ i ] == T[ j ] )
          upmin( dp[ i + 1 ][ j + 1 ], dp[ i ][ j ] );
        if( i + 1 <= N and j + 1 <= M )
          upmin( dp[ i + 1 ][ j + 1 ], dp[ i ][ j ] + 1 );
        if( i + 1 <= N )
          upmin( dp[ i + 1 ][ j ], dp[ i ][ j ] + 1 );
        if( j + 1 <= M )
          upmin( dp[ i ][ j + 1 ], dp[ i ][ j ] + 1 );
      }
}

void solve(){
  cout << dp[ N ][ M ] << endl;
}

signed main(){
  ios::sync_with_stdio( 0 );
  init();
  preprocess();
  solve();
  return 0;
}