// luogu-judger-enable-o2

#include<cstdio>

#include<cmath>

#include<algorithm>

using namespace std;

const int eps = 1e-;

int dcmp(double x) {

    if(fabs(x) < eps) return ;

    return x <  ? - : ;

}

#define Point Vector

struct Vector {

    double x, y;

    Vector(double x = , double y = ) : x(x), y(y) {};

    bool operator < (const Vector &rhs) const {

        return dcmp(x - rhs.x) ==  ? y < rhs.y : x < rhs.x;

    }

    Vector operator - (const Vector &rhs) const {

        return Vector(x - rhs.x, y - rhs.y);

    }

};

double Cross(Vector A, Vector B) {

    return A.x * B.y - A.y * B.x;

}

double dis(Point a, Point b) {

    return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));

}

int N;

Point p[], q[];

int top;

void Push(Point p) {

    while(Cross(q[top] - q[top - ], p - q[top - ]) < ) top--;

    q[++top] = p;

}

void Andrew() {

    q[] = q[top = ] = p[];

    for(int i = ; i <= N; i++) Push(p[i]);

    for(int i = N - ; i; --i)  Push(p[i]);

}

int main() {

    scanf("%d", &N);

    for(int i = ; i <= N; i++) scanf("%lf%lf", &p[i].x, &p[i].y);

    sort(p + , p + N + );

    Andrew();

    double ans = ;

    for(int i = ; i < top; i++)

        ans += dis(q[i], q[i + ]);

    printf("%.2lf", ans);

    return ;

}