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

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

static const double EPS = 1e-8;
static const double PI = 4.0 * atan(1.0);
static const double PI2 = 8.0 * atan(1.0);

#define REP(i,n)	for(int i=0;i<(int)n;++i)
#define ALL(c)		(c).begin(),(c).end()
#define CLEAR(v)	memset(v,0,sizeof(v))
#define MP(a,b)		make_pair((a),(b))
#define ABS(a)		((a)>0?(a):-(a))
#define FOR(i,s,n)	for(int i=s;i<(int)n;++i)

int N;
double X[1000], Y[1000];
vector<int> es[1000];
vector<vector<int>> conn;
bool ved[1000];

void make_conn(int v, vector<int> &vs) {
	if (ved[v]) return;
	ved[v] = true;
	vs.push_back(v);
	REP(i, es[v].size()) make_conn(es[v][i], vs);
}

int main(int argc, char **argv) {
	cin >> N;
	REP(i, N) cin >> X[i] >> Y[i];
	REP(i, N) FOR(j, i + 1, N) if (hypotl(X[j] - X[i], Y[j] - Y[i]) <= 10 + EPS) {
		es[i].push_back(j);
		es[j].push_back(i);
	}
	CLEAR(ved);
	REP(i, N) if (!ved[i]) {
		vector<int> vs;
		make_conn(i, vs);
		conn.push_back(vs);
	}
	double res = 1;
	REP(i, conn.size()) {
		double mv = 0;
		int mj = -1, mk = -1;
		REP(j, conn[i].size()) FOR(k, j + 1, conn[i].size()) {
			int a = conn[i][j], b = conn[i][k];
			double d = hypotl(X[b] - X[a], Y[b] - Y[a]);
			if (d > mv) {
				mv = d;
				mj = j;
				mk = k;
			}
		}
		res = max(res, mv + 2);
	}
	cout << fixed << setprecision(10) << res << endl;
	return 0;
}