#include <bits/stdc++.h>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef complex<double> P;

struct UnionFind
{
  vector<int> rank;
  vector<int> par;
  UnionFind(int n) {
    rank.resize(n), par.resize(n);
    rep(i, n) { par[i] = i; rank[i] = 0; }
  }
  
  int find(int x) {
    if(par[x] == x) { return x; }
    else { return par[x] = find(par[x]); }
  }
  
  void unite(int x, int y) {
    x = find(x), y = find(y);
    if(x == y) { return; }
    
    if(rank[x] < rank[y]) { par[x] = y; }
    else {
      par[y] = x; 
      if(rank[x] == rank[y]) { rank[x] ++; }
    }
  }

  bool same(int x, int y) {
    return find(x) == find(y);
  }
  
};

int main() {

  int N; cin >> N;
  
  if(N == 0) {
    cout << 1 << endl;
    return 0;
  }
  
  vector<P> ps(N);
  rep(i, N) {
    double x, y; cin >> x >> y;
    ps[i] = P(x, y);
  }
  
  UnionFind uf(N);
  
  rep(i, N) REP(j, i, N) {
    if(abs(ps[i]-ps[j]) <= 10.) {
      uf.unite(i, j);
    }
  }
  
  
  double ans = 0.;
  rep(i, N) REP(j, i, N) {
    if(!uf.same(i, j)) continue;
    ans = max(ans, abs(ps[i]-ps[j]) + 2);
  }
  
  printf("%.10f\n", ans);
  
  return 0;
}