#include <bits/stdc++.h>
#define MAXN  2000005
#define ll long long
#define F first
#define S second
#define MOD 1000000007
#define ll long long

using namespace std;

ll a, b, c, d;

void solve()
{
    cin >> a >> b >> c >> d;
    ll ans = (b - 1ll*c * d);
    if(ans == 0)
    {
        cout << -1;
        return;
    }
    if(-a*1ll/ ans < 0)
    {
        cout << -1 ;
        return;
    }
    ans = -a / ans + ((a % ans) ? 1 : 0);
    cout << ans << "\n";
}

int main()
{
    ios_base :: sync_with_stdio(0);
    cin.tie();
    cout.tie();
    if(fopen(".inp", "r"))
    {
        freopen(".inp", "r", stdin);
        freopen(".out", "w", stdout);
    }
    int t;
    t = 1;
    //cin >> t;
    while(t--)
    {
        //cerr << t << '\n';
        solve();
    }
    return 0;
}

#include <bits/stdc++.h>
using namespace std;

using uli = unsigned long int;
using ll = long long;

#define rep(i, x) for (int i = 0; i < x; i++)
#define REP(i, x) for (int i = 1; i <= x; i++)

#define chmin(a, b) \
  if (a > b) a = b
#define chmax(a, b) \
  if (a < b) a = b

int main() {
  double V, T, S, D;
  cin >> V >> T >> S >> D;

  double t = D / V;
  if (t >= T && t <= S)
    cout << "No" << endl;
  else
    cout << "Yes" << endl;
  return 0;
}
