#include <stdio.h>

int main(){
  int A,B,C,D;
  
  scanf("%d %d %d %d",&A,&B,&C,&D);
  
  while(1){
    C-=B;
    if(C <= 0) {
      puts("Yes\n");
      break;
    }
    A-=D;
    if(A <= 0){
      puts("No\n");
      break;
    }
  }
  
  return 0;
}