#include <bits/stdc++.h>
#define ld long double
#define EPS 1E-15L
using namespace std;
ld a, b, c, d;
ld f(ld x)
{
    return a * x * x * x + b * x * x + c * x + d;
}
int main()
{
    cin >> a >> b >> c >> d;
    ld l = -1E9L, r = 1E9L;
    for (int i = 0; i < 1000; i++)
    {
        ld m = (l + r) / 2.0L;
        if (f(m) < EPS && a > 0)
            l = m;
        else if (f(m) >= EPS && a > 0)
            r = m;
        else if (f(m) < EPS && a < 0)
            r = m;
        else if (f(m) >= EPS && a < 0)
            l = m;
    }
    cout << fixed << setprecision(20) << l << endl;
    return 0;
}