#include <iostream>
#include <iomanip>
#include <cmath>
#include <algorithm>
#include <cassert>

// [20 Sep 2005, by yuizumi]
// It is recommended to set EPS to about 10^(-8) (1e-8) when generating
// the judge's output; the copmiler option -D may be useful.

#ifndef EPS
#define EPS (1e-6)      // much enough to reduce an error to 10^(-3)
#endif

using namespace std;

class ellipse_t
{
private:
    double a, b;
public:
    ellipse_t(void) {
    }
    ellipse_t(double a, double b) : a(a), b(b) {
    }
public:
    double operator() (double x) const {
        return b * sqrt(a * a - x * x) / a;
    }
};

static ellipse_t f, g;

double integrate(double xmin, double xmax)
{
    double Smax = min(f(xmin), g(xmin)) * (xmax - xmin);
    double Smin = min(f(xmax), g(xmax)) * (xmax - xmin);

    if(fabs(Smax - Smin) >= EPS) {
        double x = (xmin + xmax) / 2.0;
        return integrate(xmin, x) + integrate(x, xmax);
    }
    else {
        return (Smax + Smin) / 2.0;
    }
}

int main(void)
{
    int n;
    cin >> n;

    while(n-- > 0) {
        double a1, b1, a2, b2;
        cin >> a1 >> b1 >> a2 >> b2;
		assert(a1 > b1);
		assert(a2 < b2);

        f = ellipse_t(a1, b1);
        g = ellipse_t(a2, b2);

        // output six decimal digits for judge's output
        cout << fixed << setprecision(6);
        cout << integrate(0.0, min(a1,a2)) * 4.0 << endl;
    }
}