#include <iostream>
#include<sstream>
#include<string>
#include<vector>
#include <cmath>
#include <limits>
#include <queue>
#include<algorithm>
#include<cstring>
#include <cstdlib>
#include <cstdio>
#include <set>
#include <iomanip>
#include <map>
#include <stack>
#include <memory>
#include <numeric>
#include <type_traits>
 
using namespace std;
 
#define rep(i,n) for (int (i)=0;(i)<(n);i++)
typedef long long ll;





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

  return 0;
}