#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)
        {
            printf("Yes\n");break;
        }
        a=a-d;
        if(a<=0)
        {
            printf("No\n");break;
        }
    }
    return 0;
}
