#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(c<=0) printf("Yes");
    else printf("No");
    return 0;
}