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
//package abc157.C;

import java.util.Scanner;

public class Main {
	
	public static void main (String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt(), m = sc.nextInt();
		
		int[] s = new int[m];
		int[] c = new int[m];
		
		for (int i = 0; i < m; i++) {
			s[i] = sc.nextInt();
			c[i] = sc.nextInt();
		}
		
		for (int i = 0; i < m; i++) {
			if (n != 1 && s[i] == 1 && c[i] == 0) {
				System.out.println(-1);
				return;
			}
			for (int j = 0; j < i; j++) {
				if (s[i] == s[j] && c[i] != c[j]) {
					System.out.println(-1);
					return;
				}
			}
		}
		
		for (int i = 0; i < 1000; i++) {
			String tmp = "" + i;
			if (tmp.length() != n) continue;
			boolean b = true;
			for (int j = 0; j < m; j++) {
				if (tmp.charAt(s[j] - 1) - '0' != c[j]) {
					b = false;
					break;
				}
			}
			if (b == false) continue;
			System.out.println(i);
			return;
		}
	}
	
}
