#include <iostream>
#include <algorithm>
using namespace std;

int main(){
    int i,j,n,temp,pp;
    cin >> n;
    int a[n];
    for(i=0;i<n;i++)
        {
        cin>>a[i];
    }
    sort(&a[0],&a[n]);
    i=0;
    int count,max=0;
    while(i<n)
        {
        count=0;
        temp=a[i];
        while(a[i]==temp){i++;count++;}
        if(a[i]==temp+1)
           {
          temp=a[i];
          while(a[i]==temp){i++;count++;}
        }
        if(count>max)max=count;
    }
    cout<<max;
}