#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <stack>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;

int main(){
  ios::sync_with_stdio(false);
  int N, M;
  int X, Y;
  cin >> N >> M;
  cin >> X >> Y;

  X--;
  Y--;
  int x, y;
  if((X/M)%2==0) x = X%M;
  else x = M-1-(X%M);
  if((Y/M)%2==0) y = Y%M;
  else y = M-1-(Y%M);

  if(x==y) cout << "YES" << endl;
  else cout << "NO" << endl;
  return 0;
}