#include <iostream>
#include <vector>
#include <cmath>

struct coor{
double x,y;
};

double X,Y,R,Ax,Ay,Bx,By;
double obsah(coor a, coor b)
{
	double x1 = a.x-X;
	double y1 = a.y-Y;
	double x2 = b.x-X;
	double y2 = b.y-Y;
	return -(x1*y2-y1*x2)/2;
}	

double dist(double x1,double y1, double x2, double y2)
{
	return std::sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}

std::pair<double, double> Xintersect(int height)
{
	double l=X;
	double r=2000;
	while(std::abs(l-r)>1e-8)
	{
		double m = (l+r)/2;
		if(dist(X,Y,m,height) > R)
			r=m;
		else l=m;	
	}
	double ret1 = r;

	l=-2000;
	r=X;
	while(std::abs(l-r)>1e-8)
	{
		double m = (l+r)/2;
		if(dist(X,Y,m,height) > R)
			l=m;
		else r=m;
	}
	std::pair<double, double> ret = {ret1, l};
	return ret;
}


std::pair<double, double> Yintersect(int width)
{
	double u=Y;
	double d=2000;
	while(std::abs(u-d)>1e-8)
	{
		double m = (u+d)/2;
		if(dist(X,Y,width,m) > R)
			d=m;
		else u=m;	
	}
	double ret1 = d;

	u=-2000;
	d=Y;
	while(std::abs(u-d)>1e-8)
	{
		double m = (u+d)/2;
		if(dist(X,Y,width,m) > R)
			u=m;
		else d=m;
	}
	std::pair<double, double> ret = {ret1, u};
	return ret;
}

double vysec(coor a, coor b)
{
	double a1 = atan2(a.y-Y, a.x-X);
	double a2 = atan2(b.y-Y, a.x-X);
	if(a1 < 0)
		a1 += 2*M_PI;
	if(a2 < 0)
		a2 += 2*M_PI;
	if(a2 < a1)
		a2 += 2*M_PI;
	return (a2-a1)*R*R/2;
}

int main()
{
	std::cin >> X >> Y >> R >> Ax >> Ay >> Bx >> By;

	if(Ay>By) std::swap(Ay,By);
	if(Ax>Bx) std::swap(Ax,Bx);

	std::vector<coor> v1;
	
	std::vector<coor> v;
	
	if(std::abs(Ay-Y)<R)
	{
	std::pair<double, double> A = Xintersect(Ay);
	if(A.first > Ax && A.first < Bx) v.push_back({A.first,Ay});
	if(A.second > Ax && A.second < Bx) v.push_back({A.second,Ay});
	if(dist(Ax,Ay,X,Y)<R) v.push_back({Ax,Ay});
	}
	if(std::abs(Ax-X)<R)
	{
	std::pair<double, double> C = Yintersect(Ax);
	if(C.second > Ay && C.second < By) v.push_back({Ax,C.second});
	if(C.first > Ay && C.first < By) v.push_back({Ax,C.first});
	if(dist(Bx,By,X,Y)<R) v.push_back({Bx,By});
	}
	if(std::abs(By-Y)<R)
	{
	std::pair<double, double> B = Xintersect(By);
	if(B.second > Ax && B.second < Bx) v.push_back({B.second,By});
	if(B.first > Ax && B.first < Bx) v.push_back({B.first,By});
	if(dist(Ax,By,X,Y)<R) v.push_back({Ax,By});
	}
	if(std::abs(Bx-X)<R)
	{
	std::pair<double, double> D = Yintersect(Bx);
	if(D.first > Ay && D.first < By) v.push_back({Bx,D.first});
	if(D.second > Ay && D.second < By) v.push_back({Bx,D.second});
	if(dist(Bx,Ay,X,Y)<R) v.push_back({Bx,Ay});
	}

	for(int i=0;i<v.size();i++)
		std::cout << v[i].x << ":" << v[i].y << std::endl;
	
	double area = 0;
	if(v.size())
	v.push_back(v[0]);
	for(int i=1;i<v.size();i++)
	{
		if(std::abs(v[i].x - v[i-1].x)<1e-6 || std::abs((v[i].y - v[i-1].y)<1e-8)
		{
			if((v[i-1].x > v[i].x && v[i].y == By) ||
			(v[i-1].x <v[i].x && v[i].y == Ay) ||
			(v[i-1].y < v[i].y && v[i].x == Bx) ||
			(v[i-1].y > v[i].y && v[i].x == Ax))
				{
					area += vysec(v[i-1],v[i]);
				}
			else
				area+=obsah(v[i-1],v[i]);	
		}
		else area+=vysec(v[i-1],v[1]);
	}
	if(v.size() == 2)
	{
		
	}
	if(v.size() < 2)
		if(X<Bx && X>Ax && Y<By && Y>Ay)
			area = 2*M_PI*R*R;
	std::cout << area << std::endl;

}