#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
typedef long long ll;
int N,M,X,Y;
int calc(int x, int g){
  if(g % 2 == 0) {
    return x % M;
  } else {
    return M - 1 - x % M;
  }
}
int main(){
  cin >> N >> M >> X >> Y;
  X--;Y--;
  int gx = X / M;
  int gy = Y / M;
  cout << (calc(X, gx) == calc(Y, gy) ? "YES" : "NO") << endl;
  return 0;
}