#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


// p(60) ~ 10^6

constexpr int INF = 1001001001;

int N;
vector<int> L, R;
vector<int> W;

vector<vector<int>> rss;

vector<int> freq;

bool check() {
  priority_queue<int, vector<int>, greater<int>> que;
  for (int i = 1; i <= N; ++i) {
    for (const int r : rss[i]) que.push(r);
    for (int j = 0; j < freq[i] * i; ++j) {
      if (!que.size()) return false;
      if (!(i <= que.top())) return false;
      que.pop();
    }
  }
  return true;
}

int ans;

void dfs(int n, int a, int w) {
  if (n == 0) {
cerr<<freq<<" "<<w<<endl;
    if (check()) {
      chmax(ans, w);
    }
  } else {
    for (chmin(a, n); a; --a) {
      ++freq[a];
      dfs(n - a, a, w + W[a]);
      --freq[a];
    }
  }
}

int main() {
  for (; ~scanf("%d", &N); ) {
    L.resize(N);
    R.resize(N);
    for (int u = 0; u < N; ++u) {
      scanf("%d%d", &L[u], &R[u]);
    }
    W.assign(N + 1, 0);
    for (int a = 1; a <= N; ++a) {
      scanf("%d", &W[a]);
    }
    
    rss.assign(N + 1, {});
    for (int u = 0; u < N; ++u) {
      rss[L[u]].push_back(R[u]);
    }
    
    ans = -INF;
    freq.assign(N + 1, 0);
    dfs(N, N, 0);
    
    if (ans > -INF) {
      printf("%d\n", ans);
    } else {
      puts("impossible");
    }
  }
  return 0;
}