#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef double db;

const int INF = 1e9;
const int N = 74;

int n;
PII lr[N];
int w[N];
bool ok = false;
int ans = -INF;

bool hasBit(LL mask, int i)
{
	return (mask >> i) & 1;
}

void rec(int sz, LL used, int cost)
{
	if (__builtin_popcount(used) == n)
	{
		ok = true;
		ans = max(ans, cost);
		return;
	}
	if (sz < n)
		rec(sz + 1, used, cost);
	int cnt = 0;
	FOR(i, 0, n)
	{
		if (!hasBit(used, i) && lr[i].F <= sz && sz <= lr[i].S && cnt < sz)
		{
			used |= 1LL << i;
			cnt++;
		}
	}
	if (cnt == sz)
		rec(sz, used, cost + w[sz]);
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cin >> n;
	FOR (i, 0, n)
		cin >> lr[i].F >> lr[i].S;
	FOR (i, 1, n)
		cin >> w[i];
	sort(lr, lr + n, [](const PII& p1, const PII& p2)
	{
		return p1.S < p2.S;
	});
	rec(1, 0, 0);
	if (!ok)
		cout << "impossible\n";
	else
		cout << ans << "\n";
	return 0;
}