#include<stdio.h>

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