#include <stdio.h>

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

  while (a > 0 || c > 0){
    a -= d;
    c -= b;
  }

  if (a <= 0) printf("No\n");
  else if (c <= 0) printf("Yes\n");

  return 0;
}