Convex Hull - Graham Scan

//Make CSP great again
//You're as beautiful as the day I lost you
#include <bits/stdc++.h>
#define TASK "CONVEXHULL"
#define Log2(x) 31 - __builtin_clz(x)
using namespace std;
const int N = 1e5;
int n;
struct TPoint
{
    long long x, y;
};
using TVector = TPoint;
TVector operator - (const TVector & a, const TVector & b)
{
    return {b.x - a.x, b.y - a.y};
}
long long operator * (const TVector & a, const TVector & b)
{
    return a.x * b.y - a.y * b.x;
}
long long distance(TPoint a, TPoint b)
{
    return (b.x - a.x) * (b.x - a.x) + (b.y - a.y) * (b.y - a.y);
}
TPoint p[N + 1];
TVector convex[N + 1];
void read()
{
    cin >> n;
    for (int i = 0; i < n; ++ i)
    {
        cin >> p[i].x >> p[i].y;
    }
    swap(*min_element(p, p + n, [](const TPoint & a, const TPoint & b)
                      {
                          if (a.y != b.y)
                          {
                              return a.y < b.y;
                          }
                          else
                          {
                              return a.x < b.x;
                          }
                      }), p[0]);
    sort(p + 1, p + n, [](const TPoint & a, const TPoint & b)
         {
             long long tmp = (a - p[0]) * (b - p[0]);
             if (tmp != 0)
             {
                 return tmp > 0;
             }
             return distance(a, p[0]) < distance(p[0], b);
         });
}
bool TurnLeft(TVector & a, TVector & b, TVector & c)
{
    return (b - a) * (c - b) > 0;
}
void solve()
{
    int m = 0;
    for (int i = 0; i < n; ++ i)
    {
        while(m >= 2 && !TurnLeft(convex[m - 1], convex[m], p[i]))
        {
            --m;
        }
        ++m;
        convex[m] = p[i];
    }
    cout << m << '\n';
    long long s = 0;
    TVector O = {0, 0};
    convex[m + 1] = convex[1];
    for (int i = 1; i <= m; ++ i)
    {
        s += convex[i] * convex[i + 1];
    }
    cout << fixed << setprecision(1) << (long double)s/ 2 << '\n';
    for (int i = 1; i <= m; ++ i)
    {
        cout << convex[i].x << ' ' << convex[i].y << '\n';
    }
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if (fopen(TASK".INP", "r"))
    {
        freopen(TASK".INP", "r", stdin);
        freopen(TASK".OUT", "w", stdout);
    }
    int t = 1;
    bool typetest = false;
    if (typetest)
    {
        cin >> t;
    }
    for (int __ = 1; __ <= t; ++ __)
    {
        //cout << "Case " << __ << ": ";
        read();
        solve();
    }
}