#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define all(x) (x).begin(),(x).end()
typedef long long lint;
 
int main() {
  int a,b,c,d;
  cin >> a >> b >> c >> d;
  
  while(1){
    c -= b;
    if(c<=0){
      cout << "Yes" << endl;
      return 0;
    }
    a -= d;
    if(a<=0){
      cout << "No" << endl;
      return 0;
    }
  }
  
}
