#include<stdio.h>

int main(){
   int A,B,C,D;
   scanf("%d %d %d %d",&A,&B,&C,&D);
   int turn = 1;
   while(A>0&&C>0){
   if(turn>0){
      C-=B;
   }else{
      A-=D;
   }
   turn *= -1;
   }
   if(A>0){
      printf("Yes\n");
   }else{
      printf("No\n");
   }
   return 0;
}
