#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

template <class T, class U>
vector<T> make_v(U size, const T& init){ return vector<T>(static_cast<size_t>(size), init); }

template<class... Ts, class U>
auto make_v(U size, Ts... rest) { return vector<decltype(make_v(rest...))>(static_cast<size_t>(size), make_v(rest...)); }

template<class T> void chmin(T &a, const T &b){ a = (a < b ? a : b); }
template<class T> void chmax(T &a, const T &b){ a = (a > b ? a : b); }

int main() {
    int n;
    cin >> n;
    map<int, int> cnt;
    vector<int> v(n);
    for (int i = 0; i < n; ++i) {
        int x;
        cin >> x;
        cnt[x]++;
        v[i] = x;
    }
    int ans = 0;
    for (auto &&i : v) {
        int val = 0;
        for (int j = 0; j < 3; ++j) {
            val += cnt[i+j];
        }
        ans = max(ans, val);
    }
    cout << ans << "\n";
    return 0;
}