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.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int m = scan.nextInt();
        int[] s = new int[m];
        int[] c = new int[m];

        for(int i = 0; i < m; i++) {
        	s[i] = scan.nextInt();
        	c[i] = scan.nextInt();

        }

        int len = 9 * (int)Math.pow(10, n - 1);
        if(n == 1)
        	len++;
        int start = 0 + (int)Math.pow(10, n - 1);
        if(n==1)
        	start = 0;

        int[] list = new int[len];
        for(int i = 0; i < list.length; i++) {
        	list[i] = start++;
        }

        for(int i = 0; i < list.length; i++) {
        	boolean f = true;
        	String temp = Integer.toString(list[i]);
        	for(int j = 0; j < m; j++) {
        		if(!(temp.substring(s[j] - 1, s[j]).equals(String.valueOf(c[j])))) {
        			f = false;
        			break;
        		}
        	}
        	if(f) {
        		System.out.println(temp);
        		return;
        	}
        }



        System.out.println(-1);
    }
}