//No.394 ハーフパイプ(1)

#include <bits/stdc++.h>
using namespace std;

int main()
{
int i;
int iSum;
int X[ 10 ];

	for( i = 0; i < 6; i++ )
		cin >> X[ i ];

	sort( X, X + 6 );

	iSum = 0;
	for( i = 1; i < 5; i++ )
		iSum += X[ i ];

	cout << iSum / 4;

	i = iSum % 4;
	if( i == 0 )
		cout << ".00" << endl;
	else if( i == 1 )
		cout << ".25" << endl;
	else if( i == 2 )
		cout << ".50" << endl;
	else
		cout << ".75" << endl;

	return 0;
}