#include<bits/stdc++.h>

using namespace std;

#define int long long
#define pb push_back
#define F first 
#define S second 

const int mol=998244353;

vector<pair<int, int>>a;
priority_queue<int, vector<int>, greater<>>ha;
vector<int>rr[65];
int ans=-1e18, tot=0, n, w[65];
void dfs(int sum, int t){
    if(sum==n){
        ans=max(ans, tot);
        return;
    }
    auto pre=ha;
    for(int i=t;i<=n-sum;i++){
        if(i!=n-sum&&n-sum-i<i) continue;
        for(int j=t+1;j<=i;j++){
            for(int ii: rr[j]) ha.push(ii);
        }
        if(ha.size()==0||ha.top()<i) continue;
        ha.pop();
        tot+=w[i];
        dfs(sum+i, i);
        ha=pre;
        tot-=w[i];
    }
}
void solve(){
    cin>>n;
    for(int i=1;i<=n;i++){
        int l, r;
        cin>>l>>r;
        rr[l].pb(r);
    }    
    for(int i=1;i<=n;i++) cin>>w[i];
    dfs(0, 0);
    if(ans==-1e18){
        cout<<"impossible\n";
        return;
    }
    cout<<ans<<"\n";
}


signed main(){
    ios::sync_with_stdio(0);cin.tie(0);
    // int t;
    // cin>>t;
    // while(t--)
    solve();
    return 0;
}