#include<stdio.h>
#include<math.h>
int main(){
    int a,b,c,d;
    scanf("%d %d %d %d",&a,&b,&c,&d);
    while(a>0 && c>0){
        c = c - b;
        if(c<=0)break;
        a = a - d;
    }
    if(a<=0)printf("No");
    else printf("Yes");
    return 0;
}