#include <bits/stdc++.h>
using namespace std;
#define maxn 70
#define ll long long
ll w[maxn], maxx = LLONG_MIN;
int  n, cnt[maxn], tot;

struct edge
{
    int l, r;
} b[maxn];

vector<int> to[maxn];
priority_queue<int, vector<int>, greater<int> > p;
void dfs(int x, int y, ll ans)
{ // to[x] 已经入队
    priority_queue<int, vector<int>, greater<int> > p0 = p;
    priority_queue<int, vector<int>, greater<int> > p1; // 记录的是原先r的情况
    if (p.top() >= y && y >= tot)
    {
        for (int i = x + 1; i <= y; i++)
        { // 处理剩余部分全部入帐的情况
            for (int j = 0; j < to[i].size(); j++)
            {
                p.push(to[i][j]);
            }
        }
        if (p.top() <= y)
        { // 全部入队了
            maxx = max(ans + w[y], maxx);
        }
    }

    for (int i = x; i * 2 <= y; i++)
    {
        if (p.top() < i)
            break;

        if (i != x)
        {
            for (int j = 0; j < to[i].size(); j++)
            {
                p.push(to[i][j]);
            }
        }
        p1=p;
        if (p.size() >= i)
        {
            for (int j = 1; j <= i; j++)
            {
                p.pop();
            }
            dfs(i, y - i, ans + w[i]);
        }
        p = p1; // 回退
    }
    p = p0; // 回退
    return ;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        cin >> b[i].l >> b[i].r;
        to[b[i].l].push_back(b[i].r);
        tot = max(tot, b[i].l);
    }
    for(int i=1;i<=n;i++){
        cin>>w[i];
    }
    for(int i=0;i<to[1].size();i++){
        p.push(to[1][i]);
    }
    dfs(1,n,0);
    if(maxx==LLONG_MIN){
        cout << "impossible"<<endl;
    }
    else {
        cout<<maxx<<endl;
    }
	return 0;
}