#include <bits/stdc++.h>
using namespace std;


int main() {
    int n;
    cin>>n;
    map<int,int> m;
    for(int i=0;i<n;i++)
    {
        int a;
        cin>>a;
        m[a]++;
    }
    int mx=INT_MIN;
    int mxx=mx;
    for(map<int,int>::iterator i=m.begin();i!=m.end();i++)
    {
        map<int,int>::iterator j=i;
        j++;
        if(j!=m.end())
        {
            if(j->first-i->first==1)
            {
                mx=max(mx,i->second+j->second);
                
            }
            else
                mx=max(mx,i->second);
        }
        else
        {
            mx=max(mx,i->second);
        }
    }
    cout<<mx<<endl;
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    return 0;
}