#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;
    int arr[n],arrS[100]={0};
    for(int i=0;i<n;i++)
    {
        cin>>arr[i];
        arrS[arr[i]]++;
    }
    int largest=arrS[1]+arrS[2];
    for(int i=1;i<100;i++)
    {
        if(arrS[i+1]+arrS[i+2]>largest)
        {
            largest=arrS[i+1]+arrS[i+2];
        }
    }
    cout<<largest;
    return 0;
}