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

#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;

template <class T> using v = vector<T>;
using ll = long long;
using dd = long double;
using int2 = pair<int, int>;
using ll2 = pair<ll, ll>;
using dd2 = pair<dd, dd>;

#define f first
#define s second
#define all(x) begin(x), end(x)
istream &__cin = cin;
#ifdef DEV_MODE
#include "debug.h"
__cinwrapper __cin_wrapper;
#define cin __cin_wrapper
#else
#define dbg(...)
#define dbg2d(...)
#endif

template <class T1, class T2>
istream &operator>>(istream &in, pair<T1, T2> &p) {
  in >> p.first >> p.second;
  return in;
}
template <class T> istream &operator>>(istream &in, v<T> &v) {
  for (auto &x : v)
    in >> x;
  return in;
}
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

/*
 _______________________________________
( If you don't fail at least 90% of the )
( time, you're not aiming high enough.  )
(                                       )
( - Alan Kay                            )
 ---------------------------------------
        o   ^__^
         o  (oo)\_______
            (__)\       )\/\
                ||----w |
                ||     ||
*/

const bool INTERACTIVE = false;
const bool MULTITEST = false;
/******************************************************************************/

#pragma region templates

#pragma endregion templates

void solve() {
  int sum = 0;
  for (int i = 0; i < 5; i++) {
    int a, l;
    cin >> a >> l;
    sum += a * l;
  }
  sum /= 5;
  int n, kwf;
  cin >> n >> kwf;
  cout << (n * sum) / kwf;
}

int main() {
#ifdef DEV_MODE
  debug_start(INTERACTIVE, "a.txt");
#else
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
#endif
  int t;
  if (MULTITEST)
    cin >> t;
  else
    t = 1;
  while (t--)
    solve();

#ifdef DEV_MODE
  debug_exit(INTERACTIVE);
#endif
}
#ifdef DEV_MODE
#include "debug.cpp"
#endif