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.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        char[] a = new char[n];

        for (int i = 0; i < n; i++) {
            a[i] = 'x';
        }

        int m = sc.nextInt();
        for (int i = 0; i < m; i++) {
            int s = sc.nextInt() - 1;
            char c = sc.next().charAt(0);
            if (a[s] == 'x' || a[s] == c) {
                a[s] = c;
            } else {
                System.out.println("-1");
                System.exit(0);
            }
        }

        if ((a[0] == '0' || a[0] == 'x') && n == 1) {
            a[0] = '0';
        } else if (a[0] == '0') {
            System.out.println("-1");
            System.exit(0);
        } else if (a[0] == 'x') {
            a[0] = '1';
        }
        System.out.println(String.valueOf(a).replace("x", "0"));
    }
}
