#include <bits/stdc++.h>
using namespace std;
#define rep(i,j,k) for(i=j;i<=k;++i)
#define dow(i,j,k) for(i=j;i>=k;--i)
#define pr pair
#define mkp make_pair
#define fi first
#define se second
const int N=70;
int cnt[N],n,w[N],ans=1<<31,hsh[N][N];
vector<pr<int,int > >st[N],ed[N];
void dfs(int s,int n,int cur,int sum){
    if(s==n){
        int i,j,flg=1;
        priority_queue<pr<int,int> >S;
        if(sum<=ans)return;
        rep(i,1,cur){
            for(auto v:st[i]){
                S.push(v);
                hsh[v.fi][v.se]++;
            }
            int req=i*cnt[i];
            if(S.size()<req){flg=0;break;}
            rep(j,1,req){
                pr<int,int>u=S.top();S.pop();
                hsh[u.fi][u.se]--;
            }
            for(auto v:ed[i]){
                if(hsh[v.fi][v.se]){flg=0;break;}
            }
            if(flg==0)break;
        }
        if(flg){
            ans=max(ans,sum);
        }
        return;
    }
    if(s+cur>n)return;
    int i;
    for(i=0;i*(cur+1)+s<=n;++i){
        cnt[cur+1]=i;
        dfs(s+i*(cur+1),n,cur+1,sum+i*w[cur+1]);
    }
}
int main(){//freopen("in.txt","r",stdin);
    ios::sync_with_stdio(false);
    cin>>n;
    int i,j;
    rep(i,1,n){
        int l,r;cin>>l>>r;
        st[l].push_back(mkp(-r,i));ed[r].push_back(mkp(-r,i));
    }
    rep(i,1,n)cin>>w[i];
    //rep(i,1,n)w[i]=-100;
    dfs(0,n,0,0);
    if(ans>(1<<31))cout<<ans;else cout<<"impossible";
}