#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;
    vector<int> a(n);
    for(int a_i = 0;a_i < n;a_i++){
       cin >> a[a_i];
    }
    sort(a.begin(),a.end());
    int flag = 0,ans = INT_MIN,result=0;
    for(int i=1;i<n;i++)
        {
       if(a[i-1]==a[i])
           {
           result++;
       }else if(a[i-1] == a[i]-1 ){
           if(flag == 1)
               {
               if(ans<result)
                   ans = result;
               result =0;
               flag = 0;
           }else
               {
               result++;
               flag=1;
           }
       } else{
           if(ans<result)
                   ans = result;
               result =0;
               flag = 0;
       }
    }
    if(ans ==INT_MIN)
        cout<<result+1;
    else
 if(ans!=0)
    cout<<ans+1;
else
    cout<<"0";
    return 0;
}