#include <bits/stdc++.h>

using namespace std;

typedef unsigned long      ulong;
typedef unsigned long long ulonglong;

int main(int argc, char** argv)
{
	ulonglong H,W; cin >> H >> W;
	ulonglong N,K; cin >> N >> K;
	ulonglong turn = (H * W - 1) % N + 1;
	cout << ( turn==K ? "YES" : "NO" ) << endl;
}