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

using namespace std;

const double PI = atan(1) * 4;

double X[4], Y[4];

double dist(int i1, int i2)
{
    return sqrt((X[i1] - X[i2]) * (X[i1] - X[i2]) + (Y[i1] - Y[i2]) * (Y[i1] - Y[i2]));
}
double area(int i1, int i2, int i3)
{
    return fabs(X[i1] * Y[i2] + X[i2] * Y[i3] + X[i3] * Y[i1] - Y[i1] * X[i2] - Y[i2] * X[i3] - Y[i3] * X[i1]) / 2;
}

int main()
{
    for (int i = 0; i < 3; ++i)
        cin >> X[i] >> Y[i];

    X[3] = (X[1] + X[2]) / 2;
    Y[3] = (Y[1] + Y[2]) / 2;

    double result = 0;

    result += PI * (dist(0, 1) / 2) * (dist(0, 1) / 2) / 2;
    result += PI * (dist(0, 2) / 2) * (dist(0, 2) / 2) / 2;
    result -= PI * (dist(1, 2) / 2) * (dist(1, 2) / 2) / 2;
    result += area(0, 1, 2);

    cout << fixed << setprecision(6) << result << '\n';
}