#include <sstream>
#include <iostream>
#include <algorithm>
#include <unordered_map>

using namespace std;


int main(){
    int n;
    int max;
    cin >> n;
    int *mas = new int[100];
    int elem;
    for(int i = 0; i < n ; i++){
       cin >> elem;
       mas[elem]++;
    }
    max = mas[0]+mas[1];
    for (int i = 1; i < n-1 ; i++)
        if ( mas[i]+mas[i+1] > max) max = mas[i]+mas[i+1];
    cout << max ;
    return 0;
}