#include<iostream>
#include<iomanip>
#include<string>
#include<algorithm>
#include<vector>
#include<set>
#include<list>
#include<queue>
#include<math.h>
#include<bitset>
using ll = long long;
using namespace std;

int main(){
    ll h, w, n, k, t;
    cin >> h >> w >> n >> k;
    t = (h+w-1)%n;
    if (!t) t = n;
    cout << ((t == k) ? "YES" : "NO") << endl;
}