#include <stdio.h>

int main()
{
	int A, B, C, D;
	scanf("%d %d %d %d", &A, &B, &C, &D);
	while (1) {
		C -= B;
		if (C <= 0) break;
		A -= D;
		if (A <= 0) break;
	}
	if (C <= 0) printf("Yes\n");
	else printf("No\n");
	fflush(stdout);
	return 0;
}