#include <bits/stdc++.h>
using namespace std;
#define int long long

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

signed main() {
	cin.tie(0)->sync_with_stdio(0);
	int n;
	cin >> n;
	vector<pii>a(n+1);
	for(int i = 1; i<=n; i++){
		int l,r;
		cin >> l >> r;
		a[i] = {l,r};
	}
	vector<int>c(n+1);
	int k;
	cin >> k;
	map<int,int>hm;

	for(int i = 0; i<k; i++){
		int x;
		cin >> x;
		for(int i = 1; i<=n; i++){
			if(a[i].first <= x && x<=a[i].second){
				c[i]++;
			}
		}
		hm[x] = 1;
	}
	for(int i = 1; i<=n; i++){
		if(c[i] >= 3){
			cout << "impossible\n";
			return 0;
		}
	}

	vector<int>add(n+1);
	vector<int>ans;
	for(int i = 2; i<=n; i++){
		if(c[i] <= 1 && c[i-1] <= 1 && !hm.count(a[i].first) && a[i].first == a[i-1].second){
			c[i-1]++;
			c[i]++;
			ans.push_back(a[i].first);
		}
	}
	for(int i = 1; i<=n; i++){
		if(c[i] == 2){
			continue;
		}
		for(int j = a[i].first+1; j<a[i].second && c[i] < 2; j++){
			if(hm.count(j))continue;
			c[i]++;
			ans.push_back(j);
		}
	}
	cout << ans.size() << '\n';
	for(int i = 0; i<ans.size(); i++){
		cout << ans[i];
		if(i+1<ans.size())cout << ' ';
	}
	cout << '\n';

	return 0;
}