#include <bits/stdc++.h>
#include <unordered_map>
#include <unordered_set>
 
using namespace std;
 
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<bool> vb;
typedef long double ld;
const ll mod = 1e9 + 7;
struct point {double x,y;};
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
const ll inf = 1LL << 62;

void solve() {
	int avg = 0;
	rep(i,0,5) {
		int a,b; cin >> a >> b; avg += a*b;
	}
	avg /= 5;
	int n, f; cin >> n >> f;
	avg *= n;
	cout << avg / f << endl;
}

int main() {
		//ifstream in("hps.in");
		//ofstream out("hps.out");
    //int t; cin >> t;
    //rep(i,0,t)
    solve();
}