#include<stdio.h>

int main (void)
{
    int a,b,c,d;

    scanf("%d %d %d %d",&a,&b,&c,&d);

    while(1){
        c-=b;
        a-=d;

        if(c<=0){
            //win taka
            printf("Yes");
            break;

        }else if(a<=0){
            printf("No");
            break;
        }
    }



    return 0 ;
}