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) {
        try (Scanner sc = new Scanner(System.in)) {
            int N = sc.nextInt();
            int M = sc.nextInt();
            int[] s = new int[M];
            int[] c = new int[M];
            for (int i = 0; i < M; i++) {
                s[i] = sc.nextInt() - 1;
                c[i] = sc.nextInt();
            }

            for (int n = 0; n < 1000; n++) {
                if (isValid(n, N, s, c)) {
                    System.out.println(n);
                    return;
                }
            }

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

    private static boolean isValid(int n, int N, int[] s, int[] c) {
        String S = "" + n;
        if (S.length() != N) {
            return false;
        }
        for (int i = 0; i < c.length; i++) {
            if (S.charAt(s[i]) - '0' != c[i]) {
                return false;
            }
        }
        return true;
    }

}