//Problem #B from Codeforces mindcoding
#include <cmath>

#include <algorithm>
#include <fstream>
#include <iostream>
#include <vector>
using namespace std;

#ifdef __APPLE__
#define DEBUG 1
#else
#define DEBUG 0
#endif

#define fi first
#define se second

const int inf = 0x3f3f3f3f;

const double pi = 3.14159265358979;

double x[3], y[3];

double dist(int a, int b) {
	return sqrt((x[a]-x[b])*(x[a]-x[b]) + (y[a]-y[b])*(y[a]-y[b]));
}

int main() {
	double rez = 0;
	for (int i = 0; i < 3; ++i) {
		cin >> x[i] >> y[i];
	}
 	double c = dist(0, 1);
	double a = dist(1, 2);
	double b = dist(0, 2);
	rez = pi * (b * b + c * c - a * a) / 8.0;
	double sp = (a + b + c) / 2;
	rez += sqrt(sp*(sp-a)*(sp-b)*(sp-c));
	cout << rez << '\n';
    return 0;
}