#include <algorithm>
#include <bitset>
#include <climits>
#include <iostream>
#include <map>
#include <string>
#include <vector>

using namespace std;
using ll = long long int;

int main() {
  ll A, B, C, D;
  cin >> A >> B >> C >> D;
  ll t = (C + B - 1) / B;
  ll s = (A + D - 1) / D;

  if (t > s) {
    printf("No\n");
  } else {
    printf("Yes\n");
  }
}