#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;
    vector<int> digits(100, 0);
    for (int i = 0; i < n; ++i) {
        int x;
        cin >> x;
        ++digits[x];
    }
    int sum = 0;
    for(int i = 0; i < 99; ++i) {
        if (digits[i] + digits[i+1] > sum)
            sum = digits[i] + digits[i+1];
    }
    cout << sum;
    return 0;
}