#include<stdio.h>
int main(void){
    long long int a,b,c,d;
    scanf("%lld %lld %lld %lld",&a,&b,&c,&d);
    long long int taka=a,aoki=c;
    while(1){
      aoki-=b;
      taka-=d;
      if(aoki<=0 && taka>0){
        printf("Yes");
        break;
      }else if(taka<=0 && aoki>0){
        printf("No");
        break;
      }
    }
    return 0;
}