#include <stdio.h>
#define MIN(x, y) (((x) > (y)) ? (y) : (x))
#define ABS(x) ((x) >= 0 ? (x) : (-(x)))

// int m[10000];
int main()
{
  int a, b, c, d;
  scanf("%d %d %d %d", &a, &b, &c, &d);

  while (1)
  {
    c -= b;
    if (c <= 0)
    {
      printf("Yes");
      return 0;
    }
    a -= d;
    if (a <= 0)
    {
      printf("No");
      return 0;
    }
  }

  return 0;
}