#include <cstdio>
#include <algorithm>
using namespace std;
 
int stack[120005],head;
struct punct {
    double x,y;
};
punct v[120005];
int n;
 
inline void push(int x) {
    stack[++head] = x;
}
 
inline double panta(punct a,punct b,punct c) {
    return ((b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x));
}
 
bool cmp(punct a,punct b) {
    return (panta(v[1],a,b) < 0);
}
 
int main() {
    freopen("infasuratoare.in","r",stdin);
    freopen("infasuratoare.out","w",stdout);
    scanf("%d",&n);
    for (int i=1;i<=n;i++) {
        scanf("%lf %lf",&v[i].x,&v[i].y);
        if (v[i].x <= v[1].x) {
            if (v[i].x < v[1].x) swap(v[1],v[i]);
            else if (v[i].y < v[1].y) swap(v[1],v[i]);
        }
    }
    sort(v+2,v+n+1,cmp);
    push(1);
    push(2);
    for (int i=3;i<=n;i++) {
        while (panta(v[stack[head-1]],v[stack[head]],v[i]) > 0) head--;
        push(i);
    }
    printf("%d\n",head);
    for (int i=head;i>=1;i--) {
        printf("%lf %lf\n",v[stack[i]].x,v[stack[i]].y);
    }
    return 0;
}
#include <cstdio>
#include <algorithm>
using namespace std;
 
int stack[120005],head;
struct punct {
    double x,y;
};
punct v[120005];
int n;
 
inline void push(int x) {
    stack[++head] = x;
}
 
inline double panta(punct a,punct b,punct c) {
    return ((b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x));
}
 
bool cmp(punct a,punct b) {
    return (panta(v[1],a,b) < 0);
}
 
int main() {
    freopen("infasuratoare.in","r",stdin);
    freopen("infasuratoare.out","w",stdout);
    scanf("%d",&n);
    for (int i=1;i<=n;i++) {
        scanf("%lf %lf",&v[i].x,&v[i].y);
        if (v[i].x <= v[1].x) {
            if (v[i].x < v[1].x) swap(v[1],v[i]);
            else if (v[i].y < v[1].y) swap(v[1],v[i]);
        }
    }
    sort(v+2,v+n+1,cmp);
    push(1);
    push(2);
    for (int i=3;i<=n;i++) {
        while (panta(v[stack[head-1]],v[stack[head]],v[i]) > 0) head--;
        push(i);
    }
    printf("%d\n",head);
    for (int i=head;i>=1;i--) {
        printf("%lf %lf\n",v[stack[i]].x,v[stack[i]].y);
    }
    return 0;
}