#include<stdio.h>

int main()
{
  int a, b, c, d;
  int cnt = 0;

  scanf("%d %d %d %d", &a, &b, &c, &d);
  
  while(1)
  {
    ++cnt;
    
    if(cnt % 2 == 1)
      c -= b;
    
    else
      a -= d;
    
    if(a <= 0)
    {
      printf("No");
      break;
    }
    
    else if(c <= 0)
    {
      printf("Yes");
      break;
    }
  }

  return 0;
}