#include<bits/stdc++.h>

using namespace std;


const int maxn = 60;
int w[maxn], l[maxn], r[maxn];
vector<int>rl[maxn];
int n, ans, tmp; 
multiset<int>s;
void dfs(int res, int mx, bool type){
	if(res == 0){
		ans = max(ans, tmp);
		return;
	}
	if(mx <= 0)return;
	// cout << "dfs::::"  << res << " " << mx << endl;
	if(type)for(int l : rl[mx])s.insert(l);
	// for(int x : s)cout << x << " "; cout << endl;
	
	if(s.size() >= mx){
		vector<int>t;

		// cout << "pre";
	// for(int x : s)cout << x << " "; cout << endl;
		// cout << "del:" << endl;

		for(int i = 1; i <= mx; ++i){
			auto it = --s.end();
			t.push_back(*it);
			// cout << *it << " ";
			s.erase(it);
		}
		// cout << endl;
		// cout << "deld:";
	// for(int x : s)cout << x << " "; cout << endl;

		tmp += w[mx];
		assert(res - mx >= 0);
		dfs(res - mx, mx, 0);
		tmp -= w[mx];
		while(!t.empty()){
			s.insert(t.back());
			t.pop_back();
		}
	
		// cout << "insd" << endl;
		// for(int x : s)cout << x << " "; cout << endl;

	}

	if(s.size() && *(--s.end()) >= mx){
	// cout << "dfsreturn::::"  << res << " " << mx << endl;
		if(type)for(int l : rl[mx])s.erase(s.find(l));
	// for(int x : s)cout << x << " "; cout << endl;
		return;
	}else dfs(res, mx - 1, 1);
	// cout << "dfsreturn::::"  << res << " " << mx << endl;

	if(type)for(int l : rl[mx])s.erase(s.find(l));
	// for(int x : s)cout << x << " "; cout << endl;

	return;
}
int main(){
	scanf("%d",&n);
	for(int i = 1; i <= n; ++i){
		scanf("%d%d",&l[i],&r[i]);
		rl[r[i]].push_back(l[i]);
	}
	for(int i = 1; i <= n; ++i)scanf("%d",&w[i]);
	ans = INT_MIN;
	dfs(n, n, 1);
	if(ans == INT_MIN)printf("impossible");
	else printf("%d\n",ans);
	return 0;
}