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();

        Integer a[] = new Integer[4];
        a[0] = null; a[1] = null; a[2] = null; a[3] = null;

        for (int i = 0; i < m; i++) {
            int s = scan.nextInt();
            int c = scan.nextInt();
            if (a[s] == null || a[s] == c) {
                a[s] = c;
            } else {
                System.out.println(-1);
                return;
            }
        }

        for (int i = 0; i < 1000; i++) {
            String s = String.valueOf(i);
            int len = s.length();
            if (len == n &&
                (a[1] == null || Integer.valueOf(s.substring(0,1)) == a[1]) &&
                (len >= 2 ? (a[2] == null || Integer.valueOf(s.substring(1,2)) == a[2]) : true) &&
                (len >= 3 ? (a[3] == null || Integer.valueOf(s.substring(2,3)) == a[3]) : true)) {
                    System.out.println(i);
                    return;
                }
        }

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