#include <bits/stdc++.h>
#define rep(i, x) for(ll i = 0; i < x; i++)
using ll = long long;
using namespace std;

int main() {
    int s[6];
    rep(i,6) cin >> s[i];
    double ans = (s[1] + s[2] + s[3] + s[4]) / 4;
    cout << fixed << setprecision(2) << ans << endl;
    return 0;
}