#include <cstdio>
#include <iostream>
#include <vector>
#include <queue>
#include <algorithm>
#include <numeric>
#include <cassert>

using namespace std;
using ll = long long;
constexpr ll TEN(int n) { return (!n) ? 1 : 10 * TEN(n-1); }


int main() {
    int h, w; ll n, k;
    cin >> h >> w >> n >> k;
    ll u = h+w-2;
    if (u % n == k-1) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
    return 0;
}