#include <bits/stdc++.h>
using namespace std;
#define V vector
#define pb push_back
#define all1(x) (x).begin() + 1, (x).end();
#define all0(x) (x).begin(), (x).end();
typedef long long LL;

const LL INFLL = 1e18 + 10;

void solve() {
    int n; cin >> n;
    V<int> w(n + 1);
    V<V<int>> hav(n + 1);
    for(int i = 1; i <= n; i++) {
        int l, r; cin >> l >> r;
        hav[l].pb(r);
    }
    for(int i = 1; i <= n; i++) cin >> w[i];
    LL ans = -INFLL;

    V<int> team;
    LL val = 0;

    V<int> v;

    auto dfs = [&](int x, int small, auto dfs) -> void {
        if(x == 0) {
            int now = 0;
            bool ok = 1;
            v.clear();
            int l = 0;
            for(auto x : team) {
                while(now < x) {
                    now++;
                    for(auto y : hav[now]) {
                        v.push_back(y);
                    }
                }
                while(l != v.end() - v.begin() && v[l] < x) l++;

                if(v.size() - l < x) {
                    ok = 0;
                    break;
                }
                l += x;
            }
            if(ok) {
                ans = max(ans, val);
            }
            return;
        }

        for(int i = small; i <= x; i++) {
            val += w[i];
            team.pb(i);
            dfs(x - i, i, dfs);
            val -= w[i];
            team.pop_back();
        }
    };

    dfs(n, 1, dfs);
    if(ans == -INFLL) cout << "impossible" << endl;
    else cout << ans << endl;
}

int main() {
    ios::sync_with_stdio(0), cin.tie(0);
    int t = 1;
    //cin >> t;
    while(t--) solve();
}