#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp> 
// #include <ext/pb_ds/tree_policy.hpp>
 
using namespace std;
// using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
 
typedef pair<ll, ll> pl;
typedef pair<ld,ld> pd;
typedef vector<ll> vl;
// typedef tree<ll, null_type, less<ll>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
 
 
#define G(x) ll x; cin >> x;
#define F(i, l, r) for (ll i = l; i < (r); ++i)
#define all(a) begin(a), end(a)
#define K first
#define V second
#define OK(i,j) i >= 0 && i < n && j >= 0 && j < m
 
#define NN 2000005
#define MM 5005
#define MOD 1000000007

void solve() {
 
    ll A[5], L[5];
    for(ll i=0;i<5;i++) cin >> A[i] >> L[i];
    ll N, K;
    cin >> N >> K;
    ll sum = 0;
    for(ll i=0;i<5;i++) sum += A[i]*L[i];
    sum /= 5;
    sum *= N;
    sum /= K;
    cout << sum << '\n';

    return;
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    cout << fixed << setprecision(10);

    // G(t);
    // while(t--)
        solve();

    return 0;

}