#include <stdio.h>

int main(void)
{
  int a, b, c, d;
  int ca = 0, cc = 0;
  scanf("%d %d %d %d", &a, &b, &c, &d);

  while (a > 0){
    a -= d;
    ca++; 
  }

  while (c > 0){
    c -= b;
    cc++;
  }


  if (ca > cc) printf("No\n");
  else printf("Yes\n");

  return 0;
}