#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i=0;i<n;i++)
#define rep2(i,a,b) for(int i=(a);i<(b);++i)

template<class T> inline void chmin(T& a, T b) {if (a > b) a = b;}
template<class T> inline void chmax(T& a, T b) {if (a < b) a = b;}


int main() {
  int A,B,C,D;
  cin >> A >> B >> C >> D;
  while (true) {
    C-=B;
    if (C<=0) {
      cout << "Yes\n";
      return 0;}
    A-=D;
    if (A<=0) {
      cout << "No\n";
      return 0;}
  }
}