#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 <unordered_map>

using namespace std;


int main(){
    int n;
    cin >> n;
    map<int,int> vals;
    for(int a_i = 0;a_i < n;a_i++){
        int t;
       cin >> t;
        vals[t]++;
    }
    int res=0;
    std::map<int,int>::iterator it=vals.begin();
    int prev = it->first;
    int preVal = it->second;
    res=preVal;
    for (++it; it!=vals.end(); ++it)
    {
        int cur = it->first;
        int curVal = it->second;
        if(cur-prev==1 && res<(preVal+curVal))
        {
                res=preVal+curVal;
        }
        else if(res<curVal)
            {
            res=curVal;
        }
        prev = cur;
        preVal = curVal;
    }
    cout<<res;
    return 0;
}