#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
//#include <utility>
#include <set>
#include <iostream>
//#include <memory>
#include <string>
#include <vector>
#include <algorithm>
//#include <functional>
#include <sstream>
//#include <deque>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
//#include <cctype>
#include <cstring>
//#include <ctime>
#include <iterator>
#include <bitset>
//#include <numeric>
//#include <list>
//#include <iomanip>

#if __cplusplus >= 201103L
#include <array>
#include <tuple>
#include <initializer_list>
#include <unordered_set>
#include <unordered_map>
#include <forward_list>

#define cauto const auto&
#else

#endif

using namespace std;


namespace{
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef vector<int> vint;
typedef vector<vector<int> > vvint;
typedef vector<long long> vll, vLL;
typedef vector<vector<long long> > vvll, vvLL;

#define VV(T) vector<vector< T > >

template <class T>
void initvv(vector<vector<T> > &v, int a, int b, const T &t = T()){
    v.assign(a, vector<T>(b, t));
}

template <class F, class T>
void convert(const F &f, T &t){
    stringstream ss;
    ss << f;
    ss >> t;
}


#define reep(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) reep((i),0,(n))
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define F first
#define S second
#define mkp make_pair
#define RALL(v) (v).rbegin(),(v).rend()


#define MOD 1000000007LL
#define EPS 1e-8
static const int INF=1<<24;


void mainmain(){
	int n;
	cin>>n;
	vvint vv;
	initvv(vv,n,n,INF);
	vector<pii> v(n);
	rep(i,n){
		cin>>v[i].F>>v[i].S;
	}
	rep(i,n){
		reep(j,i+1,n){
			int x=v[i].F-v[j].F;
			int y=v[i].S-v[j].S;
			if(x*x+y*y<=100){
				// cout<<"hoge\n";
				vv[i][j]=1;
				vv[j][i]=1;
			}
		}
	}
	rep(k,n){
		rep(i,n){
			rep(j,n){
				vv[i][j]=min(vv[i][j],vv[i][k]+vv[k][j]);
			}
		}
	}
	double ans=0;
	rep(i,n){
		reep(j,i+1,n){
			if(vv[i][j]!=INF){
				int x=v[i].F-v[j].F;
				int y=v[i].S-v[j].S;
				// cout<<x<<" "<<y<<endl;
				ans=max(ans,sqrt(x*x+y*y));
			}
		}
	}
	if(n==0) ans=-1;
	// cout<<ans<<endl;
	printf("%.8lf\n",ans+2);
}



}
main() try{
    mainmain();
}
catch(...){
}