#include <iostream>
#include <vector>
using namespace std;
 
int main() {
	int n;
	cin >> n;
	vector<int> bfs(n);
	vector<int> dfs(n);
	for (int i = 0; i < n; i++) { cin >> bfs[i]; }
	for (int i = 0; i < n; i++) { cin >> dfs[i]; }
 
	if (n == 1) {
		cout << 0 << endl;
		return 0;
	}
 
	// first child of node 1 must match
	if (bfs[1] != dfs[1]) {
		cout << -1 << endl;
		return 0;
	}
 
	cout << 2 * n - 3 << endl;
 
	for (int i = 1; i < n; i++) { cout << 1 << " " << bfs[i] << endl; }
 
	// skip the edge between node 1 and first child because BFS already covered it
	for (int i = 1; i < n - 1; i++) { cout << dfs[i] << " " << dfs[i + 1] << endl; }
}

import java.io.*;
import java.util.*;
 
public class Main {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
 
		int n = Integer.parseInt(br.readLine());
		int[] bfs = new int[n];
		int[] dfs = new int[n];
		String[] bfsLine = br.readLine().split(" ");
		String[] dfsLine = br.readLine().split(" ");
 
		for (int i = 0; i < n; i++) { bfs[i] = Integer.parseInt(bfsLine[i]); }
		for (int i = 0; i < n; i++) { dfs[i] = Integer.parseInt(dfsLine[i]); }
 
		if (n == 1) {
			System.out.println(0);
			return;
		}
 
		// first child of node 1 must match
		if (bfs[1] != dfs[1]) {
			System.out.println(-1);
			return;
		}
 
		System.out.println(2 * n - 3);
 
		for (int i = 1; i < n; i++) { System.out.println("1 " + bfs[i]); }
 
		// skip the edge between node 1 and first child because BFS already covered it
		for (int i = 1; i < n - 1; i++) {
			System.out.println(dfs[i] + " " + dfs[i + 1]);
		}
	}
}

n = int(input())
bfs = list(map(int, input().split()))
dfs = list(map(int, input().split()))
 
if n == 1:
	print(0)
	exit()
 
# first child of node 1 must match
if bfs[1] != dfs[1]:
	print(-1)
	exit()
 
print(2 * n - 3)
 
for i in range(1, n):
	print(1, bfs[i])
 
# skip the edge between node 1 and first child because BFS already covered it
for i in range(1, n - 1):
	print(dfs[i], dfs[i + 1])