#include<bits/stdc++.h>
using namespace std;
const int N=60;
const int inf=1<<30;
int n;
vector<int> r[N+5];
int w[N+5];
int val[N+5];
int ans;
bool work(){
    priority_queue<int,vector<int>,greater<int>> q;
    for(int i=1;i<=n;i++){
        for(auto j:r[i]) q.push(j);
        int c=val[i];
        while(!q.empty()&&c){
            int t=q.top(); q.pop();
            if(t<i) return 0;
            c--;
        }
        if(c>0) return 0;
    }
    return 1;
}
void dfs(int x,int s,int ws){
    if(s==0){
        if(work()) ans=max(ans,ws);
        return;
    }
    if(x>s) return;
    for(int j=0;j*x<=s;j++){
        val[x]=j;
        dfs(x+1,s-j*x,ws+w[x]*j);
        val[x]=0;
    }
}
int main(){
    scanf("%d",&n);
    for(int i=1,l,rr;i<=n;i++){
        scanf("%d %d",&l,&rr);
        r[l].push_back(rr);
    }
    for(int i=1;i<=n;i++)
        scanf("%d",&w[i]);
    ans=-inf;
    dfs(1,n,0);
    if(ans==-inf){
        puts("impossible");
    }
    else{
        printf("%d\n",ans);
    }
    return 0;
}