#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include<utility>
#include <unordered_map>

using namespace std;


int main(){
    int n;
    cin >> n;
    vector<int> a(n);
    for(int a_i = 0;a_i < n;a_i++){
       cin >> a[a_i];
    }
    sort(a.begin(),a.end());
    int prev = 0;
    int curSize = 1;
    int ans = 0;
    vector<pair<int,int> > v;
    pair<int,int> p;
    for(int i=1;i<n;i++){
        if(a[i]!=a[i-1]){
            ans = max(ans,curSize);
            p.first = a[i-1];
            p.second = curSize;
            v.push_back(p);
            curSize = 1;
        }else{
            curSize++;
        }
    }
    ans = max(ans,curSize);
    p.first = a[n-1];
    p.second = curSize;
    v.push_back(p);  //last group
    for(int i=1;i<v.size();i++){
        if(v[i].first == v[i-1].first+1)
            ans = max(ans,v[i].second+v[i-1].second);
    }
    cout<<ans<<endl;
    return 0;
}