#include <bits/stdc++.h>
using namespace std;
const double PI = acos(-1.0);
int main()
{
double x1, y1, r1, x2, y2, r2;
cin >> x1 >> y1 >> r1 >> x2 >> y2 >> r2;
double d = hypot(x2 - x1, y2 - y1);
if(d >= r1 + r2)
{
cout << "0\n";
return 0;
}
if(d + r1 <= r2)
{
cout << PI * r1 * r1 << "\n";
return 0;
}
if(d + r2 <= r1)
{
cout << PI * r2 * r2 << "\n";
return 0;
}
double a1 = acos((r1 * r1 + d * d - r2 * r2) / (2 * r1 * d));
double a2 = acos((r2 * r2 + d * d - r1 * r1) / (2 * r2 * d));
cout << (a1 - sin(2 * a1) / 2) * r1 * r1 + (a2 - sin(2 * a2) / 2) * r2 * r2 << "\n";
return 0;
}
