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

int main() {
	cin.tie(0)->sync_with_stdio(0);

	int n; cin >> n;
	
	set<vector<int>> s {vector<int>(n)};
	for (int _ = 0; _ < n; _++) {
		set<vector<int>> t;
		int l, r; cin >> l >> r; l--, r--;
		
		while (l <= r) {
			for (auto x : s) {
				vector<int> y = x;
				y[l]++;
				t.emplace(std::move(y));
			}
			l++;
		}
		s = std::move(t);
	}

	vector<int> w(n); for (auto &x : w) cin >> x;
	long long mx = LLONG_MIN;
	for (auto x : s) {
		long long sum = 0;
		bool ok = 1;
		for (int i = 0; i < n; i++) sum += 1LL * x[i]/(i+1) * w[i], ok &= x[i] % (i+1) == 0;
		if (ok) mx = max(mx, sum);
	}
	if (mx == LLONG_MIN) cout << "impossible\n";
	else cout << mx << '\n';
}