#include <stdio.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)break;	
	a=a-d;
	if(a<=0)break;
	}
	if(a<c)
    puts("No");
    else
    puts("Yes");
    return 0;
}    