#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 dp[N][N];

void updMax(int& a, int b)
{
	a = max(a, b);
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	FOR (i, 0, N) fill(dp[i], dp[i] + N, -2 * INF);
	
	int n;
	cin >> n;
	vector<PII> a(n);
	FOR (i, 0, n)
		cin >> a[i].F >> a[i].S;
	
	VI w(n);
	FOR (i, 0, n)
		cin >> w[i];
	
	vector<vector<PII>> f(n + 1);
	dp[1][0] = 0;
	FOR (i, 1, n + 1)
	{
		FOR (j, 0, n)
			if (a[j].F <= i)
				f[i].PB(a[j]);
		sort(ALL(f[i]), [](PII& p1, PII& p2)
		{
			return p1.S < p2.S;
		});
	}
	FOR (x, 1, n + 1)
	{
		FOR (used, 0, n + 1)
		{
			if (used == SZ(f[x]) || f[x][used].S > x)
				updMax(dp[x + 1][used], dp[x][used]);
			if (used + x <= SZ(f[x]))
				updMax(dp[x][used + x], dp[x][used] + w[x - 1]);
		}
	}
	//cerr << dp[n][n] << '\n';
	if (dp[n][n] < -INF)
		cout << "impossible\n";
	else
		cout << dp[n][n] << '\n';
	
	return 0;
}