#include<iostream>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<string>
#include<cstring>
#include<climits>
#include<functional>
#include<map>
#include<set>
using namespace std;

int main(){
	int H,W,N,K;
	cin>>H>>W>>N>>K;
	if((H*W%N-1+N)%N==K-1) puts("YES");
	else puts("NO");
	return 0;
}