// yukicoder: No.166 マス埋めゲーム
// 2019.4.26 bal4u

#include <stdio.h>

int main()
{
	int H, W, ans;
	long long N, K, hw;

	scanf("%d%d%lld%lld", &H, &W, &N, &K);
	hw = (long long)H * W;
	ans = (hw-1)/N*N+K == hw;
	puts(ans? "YES": "NO");
	return 0;
}