#include <stdio.h>
int a, b, c, d;
int main (){
	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;
		}
    }
}