#include<bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (n); ++i)
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
const int Mod = 998244353;
inline void uadd(int &a, const int &b){ a += b - Mod; a += (a>>31) & Mod; }
inline int add(int a, const int &b){ a += b - Mod; a += (a>>31) & Mod; return a; }
inline void usub(int &a, const int &b){ a -= b; a += (a>>31) & Mod; }
inline int sub(int a, const int &b){ a -= b, a += (a>>31) & Mod; return a; }
inline void umul(int &a, const int &b){ a = (int)(1ll * a * b % Mod); }
inline int mul(const int &a, const int &b){ return (int)(1ll * a * b % Mod); }
int qpow(int b, ll p){ int ret = 1; while(p){ if(p & 1) umul(ret, b); umul(b, b), p >>= 1; } return ret; }
const int fN = 10010;
int fact[fN], invfact[fN], inv[fN];
void initfact(int n){
	fact[0] = 1; for(int i = 1; i <= n; ++i) fact[i] = mul(fact[i - 1], i);
	invfact[n] = qpow(fact[n], Mod - 2); for(int i = n; i > 0; --i) invfact[i - 1] = mul(invfact[i], i);
	for(int i = 1; i <= n; ++i) inv[i] = mul(invfact[i], fact[i - 1]);
}
inline int binom(int n, int m){ return mul(fact[n], mul(invfact[m], invfact[n - m])); }

const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3fll;
template<typename T> inline void chmax(T &_a, const T &_b){ (_b>_a) ? (_a=_b) : _a; }
template<typename T> inline void chmin(T &_a, const T &_b){ (_b<_a) ? (_a=_b) : _a; }

int n, w[66];
pii p[66];

int v[66], vp = 0;
int ans = -inf;
priority_queue< int, vi, greater<int> > pq;
void calc(){
	while(!pq.empty()) pq.pop();
	int id = 0;
	int cur = 0;
	rep(i, vp){
		cur += w[v[i]];
		while(id < n && p[id].first <= v[i]) pq.push(p[id].second), ++id;
		if(pq.top() < v[i]) return ;
		rep(cc, v[i]){
			if(pq.empty()) return ;
			pq.pop();
		}
	}
	chmax(ans, cur);
}
void dfs(int cur, int x){
	if(x == n) return calc();
	if(x + cur == n || x + cur + cur <= n){
		v[vp++] = cur;
		dfs(cur, x + cur);
		--vp;
	}
	if(x + cur + 1 <= n) dfs(cur + 1, x);
}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> n;
	rep(i, n) cin >> p[i].first >> p[i].second;
	sort(p, p + n);
	for(int i = 1; i <= n; ++i) cin >> w[i];
	dfs(1, 0);
	if(ans <= -inf) cout << "impossible\n";
	else cout << ans << "\n";

	return 0;
}