#include <stdio.h>
#include <stdlib.h>

typedef struct {
    double x, y;
} Punct;

/* Comparator pentru qsort: sortare dupa x, la egalitate dupa y */
int sorteaza(const void* a, const void* b) {
    Punct* p1 = (Punct*)a;
    Punct* p2 = (Punct*)b;
    if (p1->x < p2->x) return -1;
    if (p1->x > p2->x) return  1;
    if (p1->y < p2->y) return -1;
    if (p1->y > p2->y) return  1;
    return 0;
}

/* Semn: returneaza -1, 0 sau 1 dupa semnul produsului vectorial
   ne spune daca c e la stanga, pe dreapta ab, sau coliniar       */
double orientare(Punct a, Punct b, Punct c) {
    return (b.x - a.x) * (c.y - a.y)
         - (b.y - a.y) * (c.x - a.x);
}

/* Adauga un punct in stiva, eliminand punctele care fac viraj la dreapta */
void adauga_in_stiva(Punct* stiva, int* top, Punct p) {
    while (*top >= 2 && orientare(stiva[*top - 2], stiva[*top - 1], p) <= 0)
        (*top)--;
    stiva[(*top)++] = p;
}

int main() {
    FILE* fin  = fopen("infasuratoare.in",  "r");
    FILE* fout = fopen("infasuratoare.out", "w");

    int n;
    if (fscanf(fin, "%d", &n) != 1) return 0;

    Punct* pts = (Punct*)malloc(n * sizeof(Punct));
    for (int i = 0; i < n; ++i)
        fscanf(fin, "%lf %lf", &pts[i].x, &pts[i].y);

    /* Sortam punctele dupa x, la egalitate dupa y */
    qsort(pts, n, sizeof(Punct), sorteaza);

    Punct* hull = (Punct*)malloc(2 * n * sizeof(Punct));
    int inf = 0, sup = 0;

    /* Lower hull: parcurgere stanga -> dreapta */
    for (int i = 0; i < n; i++)
        adauga_in_stiva(hull, &inf, pts[i]);

    /* Upper hull: parcurgere dreapta -> stanga
       scriem direct dupa lower hull in acelasi array               */
    for (int i = n - 2; i >= 0; i--)
        adauga_in_stiva(hull + inf, &sup, pts[i]);

    /* hull contine lower + upper, fara a repeta capetele */
    int hull_size = inf + sup;
    fprintf(fout, "%d\n", hull_size);
    for (int i = 0; i < hull_size; i++)
        fprintf(fout, "%.6f %.6f\n", hull[i].x, hull[i].y);

    free(pts);
    free(hull);
    fclose(fin);
    fclose(fout);
    return 0;
}