/*
                                                   __----~~~~~~~~~~~------___
                                  .  .   ~~//====......          __--~ ~~
                  -.            \_|//     |||\\  ~~~~~~::::... /~
               ___-==_       _-~o~  \/    |||  \\            _/~~-
       __---~~~.==~||\=_    -_--~/_-~|-   |\\   \\        _/~
   _-~~     .=~    |  \\-_    '-~7  /-   /  ||    \      /
 .~       .~       |   \\ -_    /  /-   /   ||     \    /
/  ____  /         |    \\ ~-_ /  /|- _/   .||      \  /
|~~    ~~|--~~~~--_ \     ~==-/   | \~--===~~       .\/
         '         ~-|      /|    |-~\~~       __--~~
                     |-~~-_/ |    |   ~\_   _-~            /\
                          /  \     \__   \/~                \__
                      _--~ _/ | .-~~____--~-/                  ~~==.
                     ((->/~   '.|||' -_|    ~~-/ ,              . _||
                                -_     ~\      ~~---l__i__i__i--~~_/
                                _-~-__   ~)  \--______________--~~
                              //.-~~~-~_--~- |-------~~~~~~~~
                                     //.-~~~--\
    神兽 护卫
    ACCEPTED
*/
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int, int>
#define inf 0x3f3f3f3f
#define db double
#define il inline
#define endl '\n'
const int N = 2e5 + 5;
const int mod = 998244353;
#define double long double
const double PI = acos(-1.0); // pai, 3.1415916....
typedef struct Point
{
    double x, y;
    Point(double x = 0, double y = 0) : x(x), y(y) {} 
    Point operator-(const Point &B) const { return Point(x - B.x, y - B.y); }
    double operator*(const Point &B) const { return x * B.x + y * B.y; }
} Vector;
double len(Vector A) { return sqrt(A * A); }
double Angle(Vector A, Vector B)
{
    double t = acos((A * B) / len(A) / len(B));
    return t;              // 返回 [0, π]
}
Point a[N];
void solve()
{
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> a[i].x >> a[i].y;
    a[0] = a[n];
    a[n + 1] = a[1];
    a[n + 2] = a[2];
    double ans = 0.0;
    for (int i = 1; i <= n; i++) 
    {
        ans += max(PI - Angle(a[i - 1] - a[i], a[i + 1] - a[i]) - Angle(a[i] - a[i + 1], a[i + 2] - a[i + 1]), 0.0);
    }
    ans = ans / PI;
    cout << fixed << setprecision(10) << ans << '\n';
}
signed main()
{
    // freopen("D:\\3022244240\\vscode\\txt\\in.txt", "r", stdin);
    // freopen("D:\\3022244240\\vscode\\txt\\out.txt", "w", stdout);
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    int T = 1;
    // cin >> T;
    while (T--) solve();
    return 0;
}

answer.code: In function ‘void solve()’:
answer.code:60:19: error: no matching function for call to ‘max(long double, double)’
   60 |         ans += max(PI - Angle(a[i - 1] - a[i], a[i + 1] - a[i]) - Angle(a[i] - a[i + 1], a[i + 2] - a[i + 1]), 0.0);
      |                ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/13/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/13/bits/stdc++.h:51,
                 from answer.code:23:
/usr/include/c++/13/bits/stl_algobase.h:257:5: note: candidate: ‘template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)’
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/13/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
answer.code:60:19: note:   deduced conflicting types for parameter ‘const _Tp’ (‘long double’ and ‘double’)
   60 |         ans += max(PI - Angle(a[i - 1] - a[i], a[i + 1] - a[i]) - Angle(a[i] - a[i + 1], a[i + 2] - a[i + 1]), 0.0);
      |                ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/13/bits/stl_algobase.h:303:5: note: candidate: ‘template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)’
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/13/bits/stl_algobase.h:303:5: note:   template argument deduction/substitution failed:
answer.code:60:19: note:   deduced conflicting types for parameter ‘const _Tp’ (‘long double’ and ‘double’)
   60 |         ans += max(PI - Angle(a[i - 1] - a[i], a[i + 1] - a[i]) - Angle(a[i] - a[i + 1], a[i + 2] - a[i + 1]), 0.0);
      |                ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/13/algorithm:61:
/usr/include/c++/13/bits/stl_algo.h:5795:5: note: candidate: ‘template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)’
 5795 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/13/bits/stl_algo.h:5795:5: note:   template argument deduction/substitution failed:
answer.code:60:19: note:   mismatched types ‘std::initializer_list<_Tp>’ and ‘long double’
   60 |         ans += max(PI - Angle(a[i - 1] - a[i], a[i + 1] - a[i]) - Angle(a[i] - a[i + 1], a[i + 2] - a[i + 1]), 0.0);
      |                ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/13/bits/stl_algo.h:5805:5: note: candidate: ‘template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)’
 5805 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/13/bits/stl_algo.h:5805:5: note:   template argument deduction/substitution failed:
answer.code:60:19: note:   mismatched types ‘std::initializer_list<_Tp>’ and ‘long double’
   60 |         ans += max(PI - Angle(a[i - 1] - a[i], a[i + 1] - a[i]) - Angle(a[i] - a[i + 1], a[i + 2] - a[i + 1]), 0.0);
      |                ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~