100173 A

#include <bits/stdc++.h>

using namespace std;
using Point = pair<int, int>;

const int N = 100100;

int n;
pair<int, int> a[N];

int det(int a, int b, int c, int d) { return a * d - b * c; }

int det(const Point &p, const Point &q, const Point &o) {
    return det(p.first - o.first, p.second - o.second, q.first - o.first, q.second - o.second);
}

long long dist(const Point &p, const Point &q)
{
    return 1LL * (p.first - q.first) * (p.first - q.first) + 1LL * (p.second - q.second) * (p.second - q.second);
}

int convexHull(Point *a, int n) {
    if(n < 3) return n;
    swap(*a, *min_element(a, a + n));
    sort(a + 1, a + n, [a](const Point &p, const Point &q) {
        auto d = det(p, q, a[0]);
        return d < 0 || d == 0 && dist(p, a[0]) < dist(q, a[0]);
    });
    int h = 1;
    for (int i = 2; i < n; ++i) {
        while (h > 0 && det(a[h - 1], a[h], a[i]) >= 0)
            --h;
        swap(a[++h], a[i]);
    }
    return h + 1;
}

int main() {
    scanf("%d", &n);
    for (int i = 0; i < n; ++i)
        scanf("%d%d", &a[i].first, &a[i].second);
    n = convexHull(a, n);
    printf("%d\n", n);
    for (int i = 0; i < n; ++i)
        printf("%d %d\n", a[i].first, a[i].second);
    return 0;
}