#include<stdio.h>

int main(){
   int a, b, c, d;
   scanf("%d %d %d %d", &a, &b, &c, &d);
   int judge = 1;
   while(a>0 && c>0){
      if(judge == 1){
         c -= b;
      }	else {
         a -= d;
      }
      a *= -1;
   }
   if(a>0){
      printf("Yes\n");
   } else {
      printf("No\n");
   }

   return 0;
}

