
#include <stdio.h>
#include <ctype.h>
#include <string.h>


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