#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#include <math.h>

#include <algorithm>

//#include <algorithm>

namespace Geometry {

    class point {

    public:

        double x, y;

        point() {}

        point(const point &p): x(p.x), y(p.y) {}

        point(double a, double b): x(a), y(b) {}

        point operator + (const point & p)const {

            point ret;

            ret.x = x + p.x, ret.y = y + p.y;

            return ret;

        }

        point operator - (const point & p)const {

            point ret;

            ret.x = x - p.x, ret.y = y - p.y;

            return ret;

        }

        //dot product

        double operator * (const point & p)const {

            return x * p.x + y * p.y;

        }

        //cross product

        double operator ^ (const point & p)const {

            return x * p.y - p.x * y;

        }

        bool operator < (const point & p)const {

            if (fabs(x - p.x) < 1e-) {

                return y < p.y;

            }

            return x < p.x;

        }

        double mold() {

            return sqrt(x * x + y * y);

        }

    };

    double cp(point a, point b, point o) {

        return (a - o) ^ (b - o);

    }

    class line {

    public:

        point A, B;

        line() {}

        line(point a, point b): A(a), B(b) {}

        bool IsLineCrossed(const line &l)const {

            point v1, v2;

            double c1, c2;

            v1 = B - A, v2 = l.A - A;

            c1 = v1 ^ v2;

            v2 = l.B - A;

            c2 = v1 ^ v2;

            if (c1 * c2 >= ) {

                return false;

            }

            v1 = l.B - l.A, v2 = A - l.A;

            c1 = v1 ^ v2;

            v2 = B - l.A;

            c2 = v1 ^ v2;

            if (c1 * c2 >= ) {

                return false;

            }

            return true;

        }

    };

    int Graham(point * p, point * s, int n) {

        std::sort(p, p + n);

        int top, m;

        s[] = p[];

        s[] = p[];

        top = ;

        for (int i = ; i < n; i++) { //从前往后扫

            while (top >  && cp(p[i], s[top], s[top - ]) >= ) {

                top--;

            }

            s[++top] = p[i];

        }

        m = top;

        s[++top] = p[n - ];

        for (int i = n - ; i >= ; i--) { //从后往前扫

            while (top > m && cp(p[i], s[top], s[top - ]) >= ) {

                top--;

            }

            s[++top] = p[i];

        }

        return top;

    }

}

//using namespace Geometry;

using namespace Geometry;

point p[], s[];

int main() {

#ifndef ONLINE_JUDGE

    freopen("input.txt", "r", stdin);

#endif

    int n;

    while (scanf("%d", &n) != EOF) {

        if (n == ) {

            break;

        }

        for (int i = ; i < n; i++) {

            scanf("%lf%lf", &p[i].x, &p[i].y);

        }

        int cnt = ;

        for (int i = ; i < n; i++) //去掉重复的点

            if (fabs(p[i].x - p[cnt].x) > 1e- || fabs(p[i].y - p[cnt].y) > 1e-) {

                p[++cnt] = p[i];

            }

        cnt++;

        if (cnt == ) {

            printf("0.00\n");

            continue;

        } else if (cnt == ) {

            printf("%.2lf\n", (p[] - p[]).mold());

            continue;

        }

        int top = Graham(p, s, cnt);

        double ans = ;

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

            ans += (s[i + ] - s[i]).mold();

        }

        ans += (s[top - ] - s[]).mold();

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

    }

    return ;

}