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

using i64 = long long;
const int N = 61;
int n, l[N], r[N], w[N];

vector<int> g[N];

int ans = INT_MIN;

int tot = 0;
vector<int> v;

int c[N];

bool check() {
    priority_queue<int, vector<int>, greater<int> > q;
    for(int i = 1, j = 0; i <= n; i ++) {
        while(q.size() && q.top() < i) q.pop();
        for(int x : g[i])
            q.push(x);
        while(j < v.size() && v[j] == i) {
            if(q.size() < i) return false;
            for(int t = 0; t < i; t ++) q.pop();
            j ++;
        }
    }
    return true;
}

void dfs(int lvl, int sum) {
    if(lvl > n) {
        if(tot < n) return;
        //cout << "checking ";
        //for(auto x : v) cout << x << " ";
        //cout << (check() ? "Yes" : "No") << "\n";
        if(check()) ans = max(ans, sum);
        return;
    }
    
    int cnt = 0;
    do{
        dfs(lvl + 1, sum);
        cnt ++;
        tot += lvl;
        sum += w[lvl];
        v.push_back(lvl);
    }while(tot <= n);

    while(cnt --) {
        tot -= lvl;
        v.pop_back();
    }
}

int main() {
    cin >> n;
    for(int i = 0; i < n; i ++) {
        cin >> l[i] >> r[i];
        g[l[i]].push_back(r[i]);
    }
    for(int i = 1; i <= n; i ++) cin >> w[i];

    dfs(1, 0);

    if(ans == INT_MIN) cout << "impossible";
    else cout << ans;
}