#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)(n);++i)
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;--i)
#define srep(i,s,t) for(int i=(int)(s);i<(int)(t);++i)
#define each(a,b) for(auto& (a): (b))
#define all(v) (v).begin(),(v).end()
#define len(v) (int)(v).size()
#define zip(v) sort(all(v)),v.erase(unique(all(v)),v.end())
#define cmx(x,y) x=max(x,y)
#define cmn(x,y) x=min(x,y)
#define fi first
#define se second
#define pb push_back
#define show(x) cout<<#x<<" = "<<(x)<<endl
#define spair(p) cout<<#p<<": "<<p.fi<<" "<<p.se<<endl
#define sar(a,n) cout<<#a<<":";rep(pachico,n)cout<<" "<<a[pachico];cout<<endl
#define svec(v) cout<<#v<<":";rep(pachico,v.size())cout<<" "<<v[pachico];cout<<endl
#define svecp(v) cout<<#v<<":";each(pachico,v)cout<<" {"<<pachico.first<<":"<<pachico.second<<"}";cout<<endl
#define sset(s) cout<<#s<<":";each(pachico,s)cout<<" "<<pachico;cout<<endl
#define smap(m) cout<<#m<<":";each(pachico,m)cout<<" {"<<pachico.first<<":"<<pachico.second<<"}";cout<<endl
#define double float
 
using namespace std;
 
typedef pair<int,int> P;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<double> vd;
typedef vector<P> vp;
typedef vector<string> vs;
 
const int MAX_N = 205;
constexpr double PI = acos(-1);
 
int x[MAX_N], y[MAX_N];
double d[MAX_N][MAX_N];
double mn[MAX_N];
 
// max c * x s.t. A*x <= b, x >= 0
class Simplex {
private:
    using Arr = vector<double>;
    using Mat = vector<vector<double> >;
    int* index;
    double** a;
    int row, column, L;
 
    void Set(const int n, const int cnt){
        infinity = none = false;
        row = cnt, column = n + 1;
        index = new int[row + column];
        int i, j;
        for(i = 0; i < row + column; i++){
            index[i] = i;
        }
        L = row;
        a = new double*[row + 2];
        for(i = 0; i < row + 2; i++){
            a[i] = new double[column + 4];
        }
        int id = 0;
        for(i = 0; i < n; i++){
            for(j = i+1; j < n; j++){
                if(mn[i] + mn[j] > d[i][j]){
                    a[id][i] = a[id][j] = -1;
                    a[id][column-1] = 1;
                    a[id][column] = d[i][j];
                    if(a[L][column] > a[id][column]) L = id;
                    id++;
                }
            }
        }
        for(j = 0; j < column - 1; j++){
            a[row][j] = 1;
        }
        a[row+1][column-1] = -1;
    }
 
    void solve(){
        int E, i, j;
        for(E = column - 1;;){
            if(L < row){
                swap(index[E], index[L + column]);
                a[L][E] = 1 / a[L][E];
                for(j = 0; j < column + 1; j++){
                    if(j != E) a[L][j] *= -a[L][E];
                }
                for(i = 0; i < row + 2; i++){
                    if(abs(a[i][E]) < EPS || i == L) continue;
                    for(j = -1; j < column + 1;){
                        if(++j^E) a[i][j] += a[i][E] * a[L][j];
                        if(++j^E) a[i][j] += a[i][E] * a[L][j];
                        if(++j^E) a[i][j] += a[i][E] * a[L][j];
                        if(++j^E) a[i][j] += a[i][E] * a[L][j];
                    }
                    a[i][E] = a[i][E] * a[L][E];
                }
            }
            E = -1;
            double pre = EPS;
            for(j = 0; j < column; j++){
                if(E < 0 || index[E] > index[j]){
                    if(a[row + 1][j] > pre) E = j, pre = a[row + 1][j];
                    else if(abs(a[row + 1][j]) < EPS && a[row][j] > pre) E = j, pre = a[row][j];
                }
            }
            if(E < 0) break;
            L = -1;
            for(i = 0; i < row; i++){
                if(a[i][E] < -EPS){
                    if(L < 0 || a[L][column] / a[L][E] - a[i][column] / a[i][E] < EPS) L = i;
                }
            }
            if(L < 0){
                infinity = true;
                return;
            }
        }
        if(a[row + 1][column] < -EPS){
            none = true;
            return;
        }
        x.assign(column - 1, 0);
        for(i = 0; i < row; i++){
            if(index[column + i] < column - 1) x[index[column + i]] = a[i][column];
        }
        ans = a[row][column];
    }
public:
    bool infinity, none;
    double ans;
    Arr x;
    Simplex(const int n, const int cnt){
        Set(n, cnt);
        solve();
    }
};

#define getchar getchar_unlocked

inline int in() {
    int n = 0; short c; bool flag = false;
    if((c = getchar()) < '0') flag = true; else n = c - '0';
    while ((c = getchar()) >= '0') n = n * 10 + c - '0';
    return flag ? -n : n;
}
 
int main()
{
    int n = in();
    rep(i,n){
        x[i] = in(), y[i] = in(), mn[i] = INF;
    }
    rep(i,n){
        srep(j,i+1,n){
            d[i][j] = sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
            cmn(mn[i],d[i][j]), cmn(mn[j],d[i][j]);
        }
    }
    int cnt = 0;
    rep(i,n){
        srep(j,i+1,n){
            if(mn[i] + mn[j] > d[i][j] + EPS) cnt++;
        }
    }
    Simplex sp(n, cnt);
    printf("%.12lf\n",2*sp.ans*PI);
    return 0;
}


Measured memory_bytes: 3724