#include <stdio.h>
#include <math.h>

void tut(double xo,double yo,double r,double x1,double y1,double x2,double y2);

int main (void)
{
    double xo,yo,r,x1,y1,x2,y2;
    scanf("%lf",&xo);
    scanf("%lf",&yo);
    scanf("%lf",&r);
    scanf("%lf",&x1);
    scanf("%lf",&y1);
    scanf("%lf",&x2);
    scanf("%lf",&y2);
    tut(xo,yo,r,x1,y1,x2,y2);
    return 0;
}

void tut(double xo,double yo,double r,double x1,double y1,double x2,double y2)
{
    double pi,a1,b1,a2,b2,cos,fi,fi2,otvet;
    pi=3,14159;
    a1=abs(y1-yo);
    b1=abs(x1-xo);
    a2=abs(y2-yo);
    b2=abs(x2-xo);
    cos=(a1*a2+b1*b2)/sqrt(a1*a1+b1*b1)*sqrt(a2*a2+b2*b2);
    fi=acos(cos);
    fi2=(fi*180)/pi;
    otvet=(r*r*fi2)/2;
    printf("%lf",otvet);
    return;
}