// yukicoder 225 (https://yukicoder.me/problems/no/225)
#include <algorithm>
#include <iostream>
#include <limits>
#include <string>
#define repi(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,a) repi(i,0,a)

constexpr int INF = std::numeric_limits<int>::max()>>2;

int n, m;
std::string S, T;
int dp[1001][1001];

int main()
{
  std::cin >> n >> m >> S >> T;

  std::fill( (int*)dp, (int*)(dp+n+1), INF );
  dp[0][0] = 0;
  repi( i, -1, n ) repi( j, -1, m )
  {
    if( i >= 0 && j >= 0 )
      dp[i+1][j+1] = std::min( dp[i+1][j+1], dp[i][j]+(S[i]==T[j]?0:1) );
    
    if( j >= 0 )
      dp[i+1][j+1] = std::min( dp[i+1][j+1], dp[i+1][j]+1 );
    
    if( i >= 0 )
      dp[i+1][j+1] = std::min( dp[i+1][j+1], dp[i][j+1]+1 );
  }

  printf( "%d\n", dp[n][m] );

  return 0;
}