#include <iostream>
#include <cmath>

using namespace std;

#define PI 3.1415926535

double cutarea(double r, double d)
{
	if (d >= r)
		return 0;
	if (d <= -r)
		return PI * r * r;
	return acos(d/r)*r*r - sqrt(r*r-d*d)*d;
}

double cornerarea(double r, double x, double y)
{
	//cout << r << " " << x << " " << y << endl;
	if (x >= r || y >= r)
		return 0;
	if (x <= -r && y <= -r)
		return PI * r * r;
	if (x <= -r)
		return cutarea(r, y);
	if (y <= -r)
		return cutarea(r, x);
	if (x * x + y * y >= r * r)
	{
		if (x <= 0 && y <= 0)
		{
			return PI * r * r - cutarea(r, -x) - cutarea(r, -y);
		}
		if (x <= 0 && y >= 0)
		{
			return cutarea(r, y);
		}
		if (x >= 0 && y <= 0)
		{
			return cutarea(r, x);
		}
		return 0;
	}
	double res = (4 * x * y + 2 * cutarea(r, x) + 2 * cutarea(r, y) - PI * r * r)/4;
	//cout << "returning " << res << endl;
	return res;
}

int main()
{
	double mx, my, r, ax, ay, bx, by;
	cin >> mx >> my >> r >> ax >> ay >> bx >> by;
	ax -= mx;
	bx -= mx;
	ay -= my;
	by -= my;
	double xu, xd, yu, yd;
	xu = max(ax, bx);
	xd = min(ax, bx);
	yu = max(ay, by);
	yd = min(ay, by);
	// cout << xu << " " << xd << " " << yu << " " << yd << "\n";
	double circarea = PI * r * r;
	double xusarea = cutarea(r, xu);
	double xdsarea = cutarea(r, -xd);
	double yusarea = cutarea(r, yu);
	double ydsarea = cutarea(r, -yd);
	//cout << xusarea << " " << xdsarea << " " << yusarea << " " << ydsarea << "\n";
	double c1area = cornerarea(r, xu, yu);
	double c2area = cornerarea(r, xu, -yd);
	double c3area = cornerarea(r, -xd, yu);
	double c4area = cornerarea(r, -xd, -yd);
	//cout << c1area << " "<< c2area << " "<< c3area << " "<< c4area << "\n";
	//cout << circarea << "\n";
	double res = circarea - xusarea - xdsarea - yusarea - ydsarea + c1area + c2area + c3area + c4area;
	if (res < 0)
		res = 0;
	printf("%.4f\n", res);
	return 0;
}