#include <bits/stdc++.h>
using namespace std;
const double pi = 3.14159265358979323846;
long double foo(long long int r1, long long int d, long long int r2) {
  long double cos = (r1 * r1 + d - r2 * r2) / (2 * r1 * sqrtl((long double)d));
  long double angle = acos(cos);
  return r1 * r1 * (angle - sin(angle) * cos);
}
int main() {
  int n, i, j, t;
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long int a, b, r1, c, d, r2;
  cin >> a >> b >> r1 >> c >> d >> r2;
  long long int dist = (a - c) * (a - c) + (b - d) * (b - d);
  long long int R = (r1 + r2) * (r1 + r2);
  long long int Rmin = (r1 - r2) * (r1 - r2);
  if (dist >= R)
    cout << fixed << setprecision(9) << 0.0;
  else if (dist <= Rmin)
    cout << fixed << setprecision(9) << pi * min(r1, r2) * min(r1, r2);
  else {
    long double ans = foo(r1, dist, r2) + foo(r2, dist, r1);
    cout << fixed << setprecision(9) << ans;
  }
  return 0;
}
