// In the name of Allah the most Merciful.

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

int main(void)
{
    int t , t_temp;
    map<int, int>maping;

    cin >> t;
    t_temp = t;

    while(t--){

        int in;
        cin >> in;

        maping[in]++;
    }

    int ans = 0;

    for(int i=0;i<t_temp-1;i++){

        if(ans<maping[i]+maping[i+1])ans = maping[i] + maping[i+1];
    }
    cout << ans << endl;

    return 0;
}