#include <bits/stdc++.h>
using namespace std;
priority_queue<long long int, vector<long long int>, greater<long long int>> ti;
vector<long long int> p[300005], q[300005], f(600005), b(600005), c(600005),
    a(600005);
vector<vector<long long int>> dp(505, vector<long long int>(505, -1));
map<pair<long long int, long long int>, long long int> mp;
long long int gcd(long long int a, long long int b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long int bpow(long long int a, long long int b) {
  long long int res = 1;
  while (b > 0) {
    if (b & 1) res = (res * a) % 1000000007;
    a = (a * a) % 1000000007;
    b >>= 1;
  }
  return res % 1000000007;
}
void fact(long long int i) {
  f[0] = 1;
  for (long long int k = 1; k <= i; k++) {
    (f[k] = f[k - 1] * k) %= 1000000007;
  }
}
long long int isprime(long long int n) {
  if (n == 1) return 0;
  for (long long int i = 2; i <= sqrt(n); i++)
    if (n % i == 0) return 0;
  return 1;
}
long long int find(long long int x) {
  if (f[x] == x)
    return x;
  else
    return f[x] = find(f[x]);
}
bool cmp(long long int x, long long int y) { return x < y; }
void check() {
  cout << "HI"
       << "\n";
}
long long int comb(long long int i, long long int j) {
  if (j > i) return 0;
  long long int k = f[i];
  long long int g = (f[j] * (f[i - j])) % 1000000007;
  long long int h = bpow(g, 1000000007 - 2);
  return (k * h) % 1000000007;
}
long long int cal1(long long int l, long long int r, long long int k) {
  long long int o = b[r] - b[l - 1];
  o *= k;
  long long int u = a[r] - a[l - 1];
  u += o;
  return u;
}
long long int cal2(long long int l, long long int r, long long int k) {
  long long int o = c[r] - c[l - 1];
  o *= k;
  long long int u = f[r] - f[l - 1];
  u += o;
  return u;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int n;
  cin >> n;
  vector<long long int> a(n);
  long double s = 0;
  for (long long int i = 0; i < n; i++) {
    cin >> a[i];
    s += a[i];
  }
  long double j = n;
  long long int c = 0;
  sort(a.begin(), a.end());
  for (long long int i = 0; i < n; i++) {
    if (s / j >= 4.5) break;
    if (a[i] == 5)
      continue;
    else {
      s += (5 - a[i]);
      c++;
    }
  }
  cout << c << "\n";
}
