#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;

int main() {
    
    long long H,W,N,K;
    cin >> H >> W >> N >> K;
    
    cout << ( (H-1+W-1) % N == K-1 ? "YES" : "NO " ) << endl;
    
    return 0;
}