#include <bits/stdc++.h>
#define int long long
using namespace std;
const int MOD = 1000000007;
using Graph = vector<vector<int>>;

signed main() {
  int A, B, C, D;
  cin >> A >> B >> C >> D;
  
  int cnt = 0;
  while( A > 0 && C > 0 ){
    if( cnt%2 == 0 ) C -= B;
    else A -= D;
    if( A <= 0 ){
      cout << "No" << endl;
      return 0;
    }else if( C <= 0 ){
      cout << "Yes" << endl;
      return 0;
    }
    cnt++;
  }
}