[Link] https://www.acmicpc.net/problem/7869
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#include <algorithm>
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <cstring>
#include <stack>
#include <cmath>
// #include <bits/stdc++.h>
using namespace std;
#define FASTIO ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define command_param int argc, char *argv[]
#define for0(i, n) for(int i = 0; i < n; i++)
#define for1(i, n) for(int i = 1; i < n; i++)
#define fori(s, e) for(int i = s; i < e; i++)
#define ll long long
#define endl "\n"
#define nulls '\0'
#define dkdk " "
const int MAX = 2002;
const int INF = 987654321;
int n;
int main() {
// FASTIO;
cout << fixed;
cout.precision(3);
double x1, y1, r1, x2, y2, r2;
cin >> x1 >> y1 >> r1 >> x2 >> y2 >> r2;
double s = 0;
double dis_sqr = pow(abs(x1 - x2), 2) + pow(abs(y1 - y2), 2);
if(dis_sqr >= pow(r1 + r2, 2)) {
cout << 0.000;
return 0;
}
if(dis_sqr <= pow(abs(r1 - r2), 2)) {
cout << M_PI * pow(min(r1, r2), 2);
return 0;
}
double deg1 = acos((dis_sqr + pow(r1, 2) - pow(r2, 2)) / (2*sqrt(dis_sqr)*r1));
double deg2 = acos((dis_sqr + pow(r2, 2) - pow(r1, 2)) / (2*sqrt(dis_sqr)*r2));
s+= pow(r1, 2) * deg1; // pow(p1, 2) * (2deg1) / 2;
s+= pow(r2, 2) * deg2;
s-=pow(r1, 2) * sin(2*deg1) / 2;
s-=pow(r2, 2) * sin(2*deg2) / 2;
cout << s;
return 0;
}