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