#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second

double r;
const int DEP=20;
double X,Y,R;
using dob=double;
bool wkol(dob x, dob y){
	return (x-X)*(x-X) + (y-Y)*(y-Y) <= R*R;
}

double pol(double x1, double y1, double x2, double y2, int D){
	if(D==0) return 0;
	if(wkol(x1, y1) == wkol(x2, y2)){
		return abs((x2-x1)*(y2-y1)) * wkol(x1, y1);
	}else{
		dob srx=(x1+x2)/2;
		dob sry=(y1+y2)/2;
		return pol( x1, y1, srx, sry, D-1)+
			 pol( srx, sry, x2, y2, D-1)+
			 pol( x1, sry, srx, y2, D-1)+
			 pol( srx, y1, x2, sry, D-1);
	}
}


int main(){
	ios::sync_with_stdio(0);
	double Ax, Ay, Bx,By;
	cin>>X>>Y>>R;
	cin>>Ax>>Ay>>Bx>>By;
	cout<<setprecision(5)<<fixed<<pol(min(Ax, Bx), min(Ay, By), max(Ax, Bx), max(Ay, By), DEP)<<'\n';
	return 0;
}