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

#define ll long long
#define ull unsigned long long
#define INF 0x3f3f3f3f3f3f3f3f

void solve()
{
    int n;
    cin >> n;
    vector<pair<int, int>> pr(n + 1);
    for (int i = 1; i <= n; i++)
    {
        cin >> pr[i].first >> pr[i].second;
    }
    sort(pr.begin() + 1, pr.end(), [&](const pair<int, int> &a, const pair<int, int> &b)
         {
        if(a.second != b.second)
            return a.second < b.second;
        return a.first < b.first; });
    vector<int> w(n + 1);
    for (int i = 1; i <= n; i++)
    {
        cin >> w[i];
    }
    vector<ll> dp(n + 1, -INF);
    dp[0] = 0;
    for (int i = 1; i <= n; i++)
    {
        int nl = -INF, nr = INF, np = 0;
        bool havesol = 0;
        for (int j = i; j >= 1; j--)
        {
            np++;
            nl = max(nl, pr[j].first);
            nr = min(nr, pr[j].second);
            if(np >= nl && np <= nr)
            {
                dp[i] = max(dp[i], dp[j - 1] + w[i - j + 1]);
                havesol = 1;
            }
        }
        // if(!havesol)
        // {
        //     cout << "impossible\n";
        //     return;
        // }
    }
    if(dp[n] == -INF)
        cout << "impossible\n";
    else
        cout << dp[n] << '\n';
}

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