using System;
using System.Linq;

namespace No94{
    public class Program{
        public static void Main(string[] args){
            var sr = new StreamReader();
            //---------------------------------
            var N = sr.Next<int>();
            var R = sr.Next<int>(N, 2).Select(a => new{X = a[0], Y = a[1]}).ToArray();

            Func<int, int, int, int, double> dist = (x1, y1, x2, y2) => Math.Sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
            var uf = new UnionFind(N);

            for(var i = 0; i < N; i++){
                for(var j = i + 1; j < N; j++){
                    if(dist(R[i].X, R[i].Y, R[j].X, R[j].Y) <= 10.0) uf.Unite(i, j);
                }
            }

            var res = 1.0 + Math.Sign(N);
            for(var i = 0; i < N; i++){
                for(var j = i + 1; j < N; j++){
                    if(uf.IsSameSet(i, j)) res = Math.Max(res, 2.0 + dist(R[i].X, R[i].Y, R[j].X, R[j].Y));
                }
            }

            Console.WriteLine(res);
            //---------------------------------
        }
    }

    public class Ex{
        public static void Swap<T>(ref T left, ref T right){
            var tmp = left;
            left = right;
            right = tmp;
        }
    }

    public class UnionFind{
        private readonly int[] _rank;
        private readonly int[] _p;

        public UnionFind(int size){
            _rank = new int[size];
            _p = new int[size];

            for(var i = 0; i < size; i++){
                _rank[i] = 0;
                _p[i] = i;
            }
        }

        public void Unite(int x, int y){
            x = FindSet(x);
            y = FindSet(y);

            if(_rank[x] > _rank[y]) _p[y] = x;
            if(_rank[x] < _rank[y]) _p[x] = y;
            if(_rank[x] == _rank[y]){
                _p[x] = y;
                _rank[y]++;
            }
        }

        public bool IsSameSet(int x, int y){
            return FindSet(x) == FindSet(y);
        }

        public int FindSet(int x){
            if(_p[x] == x) return x;
            return _p[x] = FindSet(_p[x]);
        }
    }

    public class StreamReader{
        private readonly char[] _c = {' '};
        private int _index = -1;
        private string[] _input = new string[0];
        private readonly System.IO.StreamReader _sr = new System.IO.StreamReader(Console.OpenStandardInput());

        public T Next<T>(){
            if(_index == _input.Length - 1){
                _index = -1;
                while(true){
                    string rl = _sr.ReadLine();
                    if(rl == null){
                        if(typeof(T).IsClass) return default(T);
                        return (T)typeof(T).GetField("MinValue").GetValue(null);
                    }
                    if(rl != ""){
                        _input = rl.Split(_c, StringSplitOptions.RemoveEmptyEntries);
                        break;
                    }
                }
            }
            return (T)Convert.ChangeType(_input[++_index], typeof(T), System.Globalization.CultureInfo.InvariantCulture);
        }

        public T[] Next<T>(int x){
            var ret = new T[x];
            for(var i = 0; i < x; ++i) ret[i] = Next<T>();
            return ret;
        }

        public T[][] Next<T>(int y, int x){
            var ret = new T[y][];
            for(var i = 0; i < y; ++i) ret[i] = Next<T>(x);
            return ret;
        }
    }
}