#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <unordered_map>

using namespace std;

int c[105] = {};
int main(){
    int n;
    cin >> n;
    vector<int> a(n);
    for(int a_i = 0;a_i < n;a_i++){
       cin >> a[a_i];
       c[a[a_i]]++;
    }
    int cMax = c[0] + c[1], pCur = cMax;
    for (int i = 2; i <= 100; i++) {
        pCur += c[i] - c[i - 2];
        cMax = max(pCur, cMax);
    }
    cout << cMax << "\n";
    return 0;
}