#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
int n;
const int N = 110;
double a[N];
int main()
{
cin>>n;
double s = 0;
for(int i=0;i<n;i++)
{
cin>>a[i];
s += a[i];
}
if(s/n >= 4.5) cout<<0<<endl;
else
{
sort(a,a+n);
int cnt = 0;
for(int i=0;i<n;i++)
{
s -= a[i];
s += 5;
if(s/n >= 4.5)
{
cnt = i;
break;
}
}
cout<<cnt+1<<endl;
}
return 0;
}