If there is an integer not less than 0 satisfying the following conditions, print the smallest such integer; otherwise, print `-1`.

* The integer has exactly N digits in base ten. (We assume 0 to be a 1-digit integer. For other integers, leading zeros are not allowed.)
* The s_i-th digit from the left is c_i. \left(i = 1, 2, \cdots, M\right)

Constraints

* All values in input are integers.
* 1 \leq N \leq 3
* 0 \leq M \leq 5
* 1 \leq s_i \leq N
* 0 \leq c_i \leq 9

Input

Input is given from Standard Input in the following format:


N M
s_1 c_1
\vdots
s_M c_M


Output

Print the answer.

Examples

Input

3 3
1 7
3 2
1 7


Output

702


Input

3 2
2 1
2 3


Output

-1


Input

3 1
1 0


Output

-1
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		if(n == 1 && m == 0) {
			System.out.println(0);
			System.exit(0);
		}
		int[] seisu = new int[n];
		Map<Integer, Integer> sici = new HashMap<>();
		for(int i = 0; i < m; i++) {
			int s = sc.nextInt();
			int c = sc.nextInt();
			if(sici.containsKey(s)) {
				if(sici.get(s) != c) {
					System.out.println(-1);
					System.exit(0);
				}
			}
			sici.put(s, c);
			seisu[s - 1] = c;
		}

		if(!sici.containsKey(1)) {
			seisu[0] = 1;
		}

		if(n != 1 && seisu[0] == 0) {
			System.out.println(-1);
			System.exit(0);
		}

		for(int value : seisu) {
			System.out.print(value);
		}

		sc.close();
	}
}