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

const int kMaxNum = 100;

int main() {
    int n;
    cin >> n;
    
    vector<int> freq(kMaxNum + 1, 0);
    while (n--) {
        int x;
        cin >> x;
        ++freq[x];
    }
    
    int result = 0;
    for (int i = 2; i <= kMaxNum; ++i)
        result = max(result, freq[i] + freq[i - 1]);
    
    cout << result << "\n";
    return 0;
}