#include <math.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef unsigned long long int ull;
typedef long long int ll;
typedef long double ld;

int main(void) {
  int scan; // scanf result
  int a; // to input 
  int b; // to input 
  int c; // to input 
  int d; // to input 
  int takahp = 0;
  int aohp = 0;

  scan = scanf("%d", &a);
  scan = scanf("%d", &b);
  scan = scanf("%d", &c);
  scan = scanf("%d", &d);

  while (a > 0)
  {
    takahp++;
    a = a - d;
  }
  while (c > 0)
  {
    aohp++;
    c = c - b; 
  }

  if (takahp < aohp)
    printf("No");
  else
    printf("Yes");
  return (0);
}
