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 scanner = new Scanner(System.in);

        int N = scanner.nextInt();
        int M = scanner.nextInt();
        int[] num = new int[N + 1];

        for (int i = 0 ; i < M ; i++) {
            int si = scanner.nextInt();
            int ci = scanner.nextInt();

            if (N > 1 && si == 1 && ci == 0) {
                System.out.println(-1);
                return;
            }
            if (num[si] != 0 && num[si] != ci) {
                System.out.println(-1);
                return;
            }
            num[si] = ci;
        }
        if (N > 1 && num[1] == 0) num[1] = 1;

        int ans = 0;
        int digit = 1;
        for (int i = N ; i > 0 ; i--) {
            ans += num[i] * digit;
            digit *= 10;
        }

        System.out.println(ans);
    }
}
