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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int n;
    cin >> n;
    int a[100],i,temp,res;
    for(i=0;i<100;i++){
        a[i]=0;
    }
    for(i=0;i<n;i++){
        cin >> temp;
        a[temp]++;
    }
    res=0;
    for(i=2;i<n;i++){
       if(a[i]+a[i-1] > res)
           res=a[i]+a[i-1];
    }
    cout << res << endl;
    return 0;
}