#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    
    long long int n,i,min,c,a,max;
    int flag;
    
    cin>>n;
    
    vector<long long int> vec;
    
    for(i=0;i<n;i++)
        {
        cin>>a;
        vec.push_back(a);
    }
    
    sort(vec.begin(),vec.end());
    
       i=c=0;
    
       min = -10000;
    flag = 0;
    max = 2;
       while(i<n-1)
        {
           if(abs(vec[i]-vec[i+1])<=1&&!flag)
               {
               
               flag = 1;
               c = c+2;
               min = vec[i];
           }
           
           else if(abs(vec[i]-vec[i+1])<=1&&min>0&&abs(min-vec[i+1])<=1&&flag)
               {
               
               c++;
           }
           
           else{
               
               c = 0;
               flag = 0;
               min = -10000;
           }
           
           max = max>c?max:c;
           
           i++;
    }
    
   
    
    cout<<max;
    
    return 0;
}