#include <stdio.h>
 
int main(void) {

	int a, b, c, d, i;
	
	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;
}