# include <iostream>
# include <iomanip>
using namespace std;
int main()
{
	float a[11],sum=0;
	int i;
	for (i=0;i<12;i++)
	{
		cin>>a[i];
		sum=sum+a[i];
	}
	cout<<"$"<<setiosflags(ios::fixed)<<setprecision(2)<<(sum/12)<<endl;
    return 0;
}