#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;

#define l first
#define r second
#define all(x) (x).begin(), (x).end()

const int M = 77;
const int inf = 1e9;

void uax(int &x, int y) {
  x = max(x, y);
}

int n;
int w[M];
vector<int> rb[M];
int ans = -inf;
int cnt[M], boys = 0;

void add(int sz) {
  cnt[sz]++;
  boys++;
}

void rem(int sz) {
  assert(cnt[sz] > 0);
  cnt[sz]--;
  boys--;
}

void rec(int k, int s, int cur) {
  if (s == n) {
    uax(ans, cur);
    return;
  }
  if (s + k > n)
    return;

  if (boys >= k) {
    vector<int> rems;
    for (int i = 0, j = k; i < k; ++i) {
      while (cnt[j] == 0)
        ++j;
      rem(j);
      rems.push_back(j);
    }

    rec(k, s + k, cur + w[k]);

    for (int r : rems)
      add(r);
  }

  if (cnt[k] > 0)
    return;

  for (int r : rb[k + 1])
    add(r);

  rec(k + 1, s, cur);

  for (int r : rb[k + 1])
    rem(r);
}

int main() {
#ifndef ONLINE_JUDGE
  freopen("e.in", "r", stdin);
#endif
  ios_base::sync_with_stdio(false);

  cin >> n;
  for (int i = 0; i < n; ++i) {
    int l, r;
    cin >> l >> r;
    rb[l].push_back(r);
  }

  for (int i = 1; i <= n; ++i)
    cin >> w[i];

  for (int r : rb[1])
    add(r);

  rec(1, 0, 0);
  if (ans == -inf)
    cout << "impossible\n";
  else
    cout << ans << "\n";
  return 0;
}