#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;
bool con[1100][1100];

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);
  }
  
  rep(i, N) {
    REP(j, i, N) {
      if(abs(ps[i]-ps[j]) <= 10.) {
        con[i][j] = con[j][i] = 1;
      }
    }
  }
  
  rep(k, N) rep(i, N) rep(j, N) {
    if(con[i][k] && con[k][j]) {
      con[i][j] = 1;
    }
  }
  
  double ans = 0.;
  rep(i, N) REP(j, i, N) {
    if(!con[i][j]) continue;
    ans = max(ans, abs(ps[i]-ps[j]) + 2);
  }
  
  printf("%.10f\n", ans);
  
  return 0;
}