#include <stdio.h>

int main()
{
    int th,ts,ah,as;
    scanf("%d %d",&th,&ts);
    scanf("%d %d", &ah,&as);
    while(1){
        ah-=ts;
        if(ah<=0) break;
        th-=as;
        if(th<=0) break;
    }
    if(th>0) printf("Yes");
    else printf("No");
    return 0;
}