#include <bits/stdc++.h>
using namespace std;
static int LOCAL = 0;
const long long int mod = 1000000007ll;
const long long int MOD = 1000000009ll;
const long long int INF = LLONG_MAX / 10;
const int inf = INT_MAX / 10;
long long int powermod(long long int _a, long long int _b,
                       long long int _m = mod) {
  long long int _r = 1;
  while (_b) {
    if (_b % 2 == 1) _r = (_r * _a) % _m;
    _b /= 2;
    _a = (_a * _a) % _m;
  }
  return _r;
}
long long int power(long long int _a, long long int _b) {
  long long int _r = 1;
  while (_b) {
    if (_b % 2 == 1) _r = (_r * _a);
    _b /= 2;
    _a = (_a * _a);
  }
  return _r;
}
long long int add(long long int a, long long int b, long long int m = mod) {
  long long int x = a + b;
  while (x >= m) x -= m;
  return x;
}
long long int sub(long long int a, long long int b, long long int m = mod) {
  long long int x = a - b;
  while (x < 0) x += m;
  return x;
}
long long int mul(long long int a, long long int b, long long int m = mod) {
  return ((a % m) * (b % m)) % m;
}
long long int gcd(long long int a, long long int b) {
  while (a && b) a > b ? a %= b : b %= a;
  return a + b;
}
long long int lcm(long long int a, long long int b) {
  return (max(a, b) / gcd(a, b)) * min(a, b);
}
struct pair_hash {
  std::size_t operator()(const std::pair<int, int> &p) const {
    auto h1 = std::hash<long long int>{}(p.first);
    auto h2 = std::hash<long long int>{}(p.second);
    return (int)add(h1, mul(h2, h1, MOD));
  }
};
struct cmp {
  bool operator()(pair<int, pair<long long int, long long int> > const &l,
                  pair<int, pair<long long int, long long int> > const &r) {
    return l.second.first < r.second.first;
  }
} myobject;
multiset<int> second;
int main() {
  int n, x;
  cin >> n;
  double sum = 0;
  for (int i = 1; i <= n; i++) scanf("%d", &x), second.insert(x), sum += x;
  double avg = sum / n;
  int cnt = 0;
  while (!(avg >= 4.50)) {
    x = *second.begin();
    second.erase(second.begin());
    sum -= x;
    sum += 5;
    avg = sum / n;
    cnt++;
  }
  cout << cnt;
  return 0;
}
