#include <iostream>
#include <cmath>

using namespace std;

#define PI 3.1415926535

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

double cornerarea(double r, double x, double y)
{
	if (x * x + y * y >= r * r)
		return 0;
	return (4 * x * y + 2 * cutarea(r, x) + 2 * cutarea(r, y) - PI * r * r)/4;
}

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;
	if (ax > bx)
	{
		xu = ax;
		xd = bx;
	}
	else
	{
		xu = bx;
		xd = ax;
	}
	if (ay > by)
	{
		yu = ay;
		yd = by;
	}
	else
	{
		yu = by;
		yd = ay;
	}
	// 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";
	double res = circarea - xusarea - xdsarea - yusarea - ydsarea + c1area + c2area + c3area + c4area;
	printf("%.4f\n", res);
	return 0;
}