#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>
#define fr(i,beg,end) for(i=beg;i<end;i++)
#define rf(i,end,beg) for(i=end;i>beg;i--)
#define ll long long
#define pb push_back
#define MOD 1000000007
using namespace std;


int main(){
    int n, i;
    cin >> n;
    ll int arr[101];
    fr(i,0,101)
        arr[i] = 0;
    vector<int> a(n);
    for(int a_i = 0;a_i < n;a_i++){
       cin >> a[a_i];
       arr[a[a_i]]++;
    }
    ll int ans = 0;
    fr(i,0,101)
        {
        if(arr[i]>0)
            ans = max(ans,arr[i]);
        if(arr[i]>0&&arr[i+1]>0)
            ans = max(ans,arr[i]+arr[i+1]);
    }
    if(ans==0)
    {
        cout<<2;
        return 0;
    }
    cout<<ans;
    return 0;
}