#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using ld=double;
#define FOR(i,a,b) for(ll i=a;i<(ll)b;++i)
#define F(n) FOR(i,0,n)
#define FF(n) FOR(j,0,n)
#define aa first
#define bb second
#define PB push_back
#define EQ(a,b) (fabs(a-b)<=(fabs(a+b)*EPS))

#define ZERO (1e-10)


struct PT{ld x,y;}pt[20];
PT vec(PT a, PT b){return {a.x-b.x,a.y-b.y};}
struct LN{PT s,e;} ln[4];
struct CC{PT c;ld r;}C;
int P;
bool cn[20];
void fd(LN l, int f){
	PT T;
	ld t;
	switch(f){
		case 0:
			if (fabs(C.c.y-l.s.y)>C.r) return;
			t=sqrt(fabs(C.r*C.r-pow(C.c.y-l.s.y,2)));
			T={C.c.x-t,l.s.y};
			if(T.x>l.s.x&&T.x<l.e.x)pt[P++]=T;
			T.x=C.c.x+t;
			if(T.x>l.s.x&&T.x<l.e.x)pt[P++]=T;
			break;
		case 1:
			if(fabs(C.c.x-l.s.x)>C.r)return;
			t=sqrt(fabs(C.r*C.r-pow(C.c.x-l.s.x,2)));
			T={l.s.x,C.c.y+t};
			if(T.y<l.s.y&&T.y>l.e.y)pt[P++]=T;
			T.y=C.c.y-t;
			if(T.y<l.s.y&&T.y>l.e.y)pt[P++]=T;
			break;
		case 2:
			if(fabs(C.c.y-l.s.y)>C.r) return;
			t=sqrt(fabs(C.r*C.r-pow(C.c.y-l.s.y,2)));
			T={C.c.x+t,l.s.y};
			if(T.x<l.s.x&&T.x>l.e.x)pt[P++]=T;
			T.x=C.c.x-t;
			if(T.x<l.s.x&&T.x>l.e.x)pt[P++]=T;
			break;
		case 3:
			if(fabs(C.c.x-l.s.x)>C.r)return;
			t=sqrt(fabs(C.r*C.r-pow(C.c.x-l.s.x,2)));
			T={l.s.x,0};
			if(l.s.y<l.e.y)T.y=C.c.y-t;
			if(T.y>l.s.y&&T.y<l.e.y)pt[P++]=T;
			T.y=C.c.y+t;
			if(T.y>l.s.y&&T.y<l.e.y)pt[P++]=T;
			
	}
}



void pre(ld lx,ld ly, ld rx, ld ry){
	ln[P=0]={{lx,ry},{rx,ry}},ln[1]={{rx,ry},{rx,ly}};
	ln[2]={{rx,ly},{lx,ly}},ln[3]={{lx,ly},{lx,ry}};
	F(4)pt[P++]=ln[i].s,fd(ln[i],i);
}


#define dst(a,b) sqrt(pow(a.x-b.x,2)+pow(a.y-b.y,2))
#define dst2(a,b) pow(a.x-b.x,2)+pow(a.y-b.y,2)

void tst(){F(P)cn[i]=dst(pt[i],C.c)>C.r+ZERO;}
ld Xp(PT a, PT b){return a.x*b.y-a.y*b.x;}
ld Dp(PT a, PT b){return a.x*b.x+a.y*b.y;}
ld tri(PT a, PT b) { return Xp(vec(a,C.c),vec(b,C.c))/2;}
ld sec(PT a, PT b){
	ld da=dst2(a,C.c),db=dst2(b,C.c),cj=Xp(vec(a,C.c),vec(b,C.c)),
	dj=Dp(vec(a,C.c),vec(b,C.c)),D=cj/sqrt(da*db),A=asin(D);
	if(dj<-ZERO)A=A>0?M_PI-A:-M_PI-A;
	return A*C.r*C.r/2;
}

ld rci(ld lx, ld ly, ld rx, ld ry, CC&c) {
	C=c;
	pre(lx,ly,rx,ry);
	if(C.r<ZERO)return 0;
	tst();
	ld A=0;
	F(P)if(!cn[i]&&!cn[(i+1)%P])A+=tri(pt[i],pt[(i+1)%P]);
		else A+=sec(pt[i],pt[(i+1)%P]);
	return fabs(A);
}







int main(){
	ios::sync_with_stdio(0);cout.tie(0);cin.tie(0);
	ll x, y, r;
	cin >> x >> y >> r;
	ll ax, ay, bx, by;
	cin >> ax >> ay >> bx >> by;
	cout << fixed << setprecision(4);
	
	ll left = min(ax, bx);
	ll right = max(ax, bx);
	ll top = min(ay, by);
	ll bot = max(ay, by);
	CC cir;
	cir.c.x = x;
	cir.c.y = y;
	cir.r = r;
	cout << rci(left, top, right, bot, cir) << endl;
	

	return 0;
}