	#include<stdio.h>
	
	int main(){
		int a,b,c,d;
		scanf("%d %d %d %d",&a,&b,&c,&d);
		while(a > 0 && c > 0){
			a = a - d;
			c = c - b;
			if(c <= 0){
				printf("Yes");
				break;
			}
			if(a <= 0){
				printf("No");
			}
		}
		
	}