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


int main() {
    int n;
    cin>>n;
    vector<int> a;
    for(int i=0;i<n;++i)
        {
        int y;
        cin>>y;
        a.push_back(y);
    }
    sort(a.begin(),a.end());

  int maxi=0;
    for(int i=0;i<n;)
        {
        
        //for i
        int p=a[i];
        int n1=1;
        while(a[++i]==p&&i<n)
            n1++;
        int j=i;
        int n2=0;
        if(a[i]==p+1)
            {n2=1;
            while(a[++i]==p+1&&i<n)
                n2++;}
        //cout<<"for j= "<<j<<" n1 and n2 are "<<n1<<" "<<n2<<"\n";
        
         
        int n3=n1+n2;
        
        
        maxi=max(maxi,n3);
           
        i=j;
            
        }
    cout<<maxi;
    
    return 0;
}