#include <cstdio>
#include <vector>
using namespace std;

int main(){
	using std::vector;
	int H, W, N, K;
	int i;
	int cnt = 0;
	int size;
	fscanf(stdin, "%d %d %d %d", &H, &W, &N, &K);
	size = H * W;
	//vector<vector<int>> arr(H, vector<int>(W));
	for (i = 1; i <= N; i++) {
		cnt++;
		if (cnt >= size) {
			break;
		}
		if (i == N) {
			i = 0; // for next roop
		}
	}
	if (i == K) {
		printf("YES\n");
	}
	else {
		printf("NO\n");
	}
	return 0;
}