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

int main(){
  int a,b,c,d;
  cin>>a>>b>>c>>d;
  while (a>0 &&c>0){
    c-=b;
    if (c<=0) {
      cout << "Yes";
      return 0;
    }
    a-=d;
    if (a<=0) {
      cout << "No";
      return 0;
    }
  }
}