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