491B

#include <bits/stdc++.h>

using namespace std;

bool check(int sum, int n) {
    // integer representation of sum / n >= 4.5
    return sum * 10 >= n * 45;
}

int main() {
    vector<int> v;
    int sum = 0;

    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
        int x;
        cin >> x;
        v.push_back(x);
        sum += x;
    }

    sort(v.begin(), v.end());
    int ans = 0;
    while (!check(sum, n)) {
        sum += 5 - v[ans];
        ans++;
    }

    cout << ans;
}