#define _USE_MATH_DEFINES
#include<iostream>
#include<string>
#include<queue>
#include<cmath>
#include<map>
#include<set>
#include<list>
#include<iomanip>
#include<vector>
#include<random>
#include<functional>
#include<algorithm>
#include<stack>
#include<cstdio>
#include<bitset>
#include<unordered_map>
#include<climits>
#include<fstream>
using namespace std;
typedef long long ll;
typedef long double ld;
#define all(a) (a).begin(),(a).end()
#define EPS (1e-5)
#define bit(n,k) ((n>>k)&1)
const ll Mod = 1000000007;
const ll mod = 998244353;
/*struct H {
    ld x, y;
    bool operator<(const H& b) const {
        if (x != b.x) return x < b.x;
        return y < b.y;
    }
    bool operator>(const H& b) const {
        if (x != b.x) return x > b.x;
        return y > b.y;
    }
    bool operator==(const H& b) const { return x == b.x && y == b.y; }
    bool operator!=(const H& b) const { return (*this) != b; }
};*/
struct P {
    ll pos, cost;
    bool operator<(const P& b) const { return cost < b.cost; }
    bool operator>(const P& b) const { return cost > b.cost; }
};
struct B {
    ll to, cost;
};
struct E {
    ll from, to, cost;
    bool operator<(const E& b) const { return cost < b.cost; }
    bool operator>(const E& b) const { return cost > b.cost; }
};
template<typename T, typename U>
void chmin(T& a, U b) {
    if (a > b) a = b;
}
template<typename T, typename U>
void chmax(T& a, U b) {
    if (a < b) a = b;
}
template<typename T>
T max_0(T a) {
    if (a < 0) return 0;
    return a;
}
template<typename T>
T min_0(T a) {
    if (a > 0) return 0;
    return a;
}
ll read() {
    ll u;
    ll k = scanf("%lld", &u);
    return u;
}
ll gcd(ll i, ll j) {
    if (i > j) swap(i, j);
    if (i == 0) return j;
    return gcd(j % i, i);
}
ll mod_pow(ll x, ll n, ll p) {
    ll res = 1;
    while (n > 0) {
        if (n & 1) res = res * x % p;
        x = x * x % p;
        n >>= 1;
    }
    return res;
}//x^n%p
const ll Inf = 3023372036854775807;
const int inf = 1500000000;
#define int long long
//----------------------------------------------------
int n;
struct H {
    ld x, y;
    bool operator<(const H& b) const { if (x != b.x) return x < b.x; return y < b.y;}
};
struct A { ld x, y; int t; } a[200000];
bool operator<(A a, A b) { if (a.x != b.x) return a.x > b.x; return a.y > b.y; }
 
ld sgarea(A a, A b, A c) {
    return ((b.x - a.x) * (c.y - a.y) - (c.x - a.x) * (b.y - a.y)) / 2;
}
H b[400000];
signed main() {
    cin >> n;
    H sum = { 0,0 };
    for (int i = 0; i < n; i++) {
        cin >> a[i].x >> a[i].y;
        sum.x += a[i].x, sum.y += a[i].y;
        a[i].t = i;
    }
    sum.x /= n, sum.y /= n; sum.x += 0.01, sum.y -= 0.01;
    sort(a, a + n);
    for (int i = 0; i < n; i++) {
        b[i] = H{ atan2(a[i].y - sum.y, a[i].x - sum.x) ,(ld)i };
        if (b[i].x < 0) b[i].x += 2 * M_PI;
    }
    sort(b, b + n);
    for (int i = 1; i < 3; i++)for (int j = 0; j < n; j++) b[i * n + j] = b[j];
    vector<int>v;
    int s = 0;
    for (int i = 0; i < n; i++) if (b[i].y == 0) s = i;
    v.push_back(b[s].y); v.push_back(b[s + 1].y);
    for (int i = 2; i <= n; i++) {
        do {
            if (sgarea(a[v[v.size() - 2]], a[v[v.size() - 1]], a[(int)b[i + s].y]) < 0) {
                v.pop_back();
            }
            else break;
        } while (v.size() > 1);
        v.push_back(b[i + s].y);
    }
    A st = { Inf,Inf,0 };
    for (int i = 0; i < v.size(); i++) {
        if (st.y > a[v[i]].y)
            st = a[v[i]], st.t = i;
        else if (st.y == a[v[i]].y && st.x > a[v[i]].x)
            st = a[v[i]], st.t = i;
    }
    v.pop_back();
    cout << v.size() << endl;
    for (int i = 0; i < v.size(); i++) {
        cout << a[v[(i + st.t) % v.size()]].x << " " << a[v[(i + st.t) % v.size()]].y << endl;
    }
}


Measured memory_bytes: 17340