#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>using namespace std;const double eps = 1e-8;const double pi = acos(-1.0);struct Point { double x, y; Point operator - (const Point& t) const { Point tmp; tmp.x = x - t.x; tmp.y = y - t.y; return tmp; } Point operator + (const Point& t) const { Point tmp; tmp.x = x + t.x; tmp.y = y + t.y; return tmp; } bool operator == (const Point& t) const { return fabs(x-t.x) < eps && fabs(y-t.y) < eps; }}GP; double cir_area_inst(Point c1, double r1, Point c2, double r2) { double a1, a2, d, ret; d = sqrt((c1.x-c2.x)*(c1.x-c2.x)+(c1.y-c2.y)*(c1.y-c2.y)); if ( d > r1 + r2 - eps ) return 0; if ( d < r2 - r1 + eps ) return pi*r1*r1; if ( d < r1 - r2 + eps ) return pi*r2*r2; a1 = acos((r1*r1+d*d-r2*r2)/2/r1/d); a2 = acos((r2*r2+d*d-r1*r1)/2/r2/d); ret = (a1-0.5*sin(2*a1))*r1*r1 + (a2-0.5*sin(2*a2))*r2*r2; return ret;}int main(){ Point a,b; double r1,r2; scanf("%lf%lf%lf%lf%lf%lf",&a.x,&a.y,&r1,&b.x,&b.y,&r2); double area = cir_area_inst(a,r1,b,r2); printf("%.3lfn",area); return 0;}
