#include<stdio.h>
int main()
{
    int a,b,c,d,f1,f2;
    scanf("%d %d %d %d",&a,&b,&c,&d);
    if(c%b==0)
        f1=c/b;
    else
        f1=c/b+1;
    if(a%d==0)
        f2=a/d;
    else
        f2=a/d+1;
    if(f1<=f2)
        printf("Yes");
    else
        printf("No");
    return 0;
}
