#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\n");return 0;}
      a-=d;
      if(a<=0){printf("No\n");return 0;}
   }
   return 0;
}