#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:102400000,102400000")
template <class T>
inline void gmax(T &a, T b) {
  if (b > a) a = b;
}
template <class T>
inline void gmin(T &a, T b) {
  if (b < a) a = b;
}
using namespace std;
const int N = 1e5 + 10, M = 2e6 + 10, Z = 1e9 + 7, maxint = 2147483647,
          ms1 = 16843009, ms31 = 522133279, ms63 = 1061109567,
          ms127 = 2139062143;
const double PI = acos(-1.0), eps = 1e-8;
void fre() {
  freopen("/Users/luras/Desktop/in.txt", "r", stdin);
  freopen("/Users/luras/Desktop/out.txt", "w", stdout);
}
const int INF = 1e9;
int casenum, casei;
struct circle {
  long double x, y, r;
} p1, p2;
long double sqr(long double x) { return x * x; }
long double dis(circle a, circle b) {
  return sqrt(sqr(a.x - b.x) + sqr(a.y - b.y));
}
long double solve(circle a, circle b) {
  long double d = dis(a, b);
  if (d >= a.r + b.r) return 0;
  if (d <= fabs(a.r - b.r)) {
    long double r = min(a.r, b.r);
    return PI * r * r;
  }
  long double ang1 = acos((a.r * a.r + d * d - b.r * b.r) / (2. * a.r * d)) * 2;
  long double ang2 = acos((b.r * b.r + d * d - a.r * a.r) / (2. * b.r * d)) * 2;
  double tmp1 = 0.5 * ang1 * a.r * a.r - 0.5 * a.r * a.r * sin(ang1);
  double tmp2 = 0.5 * ang2 * b.r * b.r - 0.5 * b.r * b.r * sin(ang2);
  long double ret = tmp1 + tmp2;
  return ret;
}
int main() {
  cin >> p1.x >> p1.y >> p1.r >> p2.x >> p2.y >> p2.r;
  cout << setprecision(15) << solve(p1, p2) << endl;
  return 0;
}
