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.ArrayList;
import java.util.List;
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];
    int res = 0;

    for (int i = 0; i < n; i++) {
      num[i] = -1;
    }

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

      if (num[s - 1] == -1) {
        num[s - 1] = c;
      } else if (num[s - 1] != c) {
        res = -1;
        break;
      }
    }

    if (res != -1) {
      if (n > 1 && num[0] == 0) {
        res = -1;
      } else {
        if(n > 1 && num[0] == -1) {
          num[0] = 1;
        }
        for (int i = 0; i < n; i++) {
          if (num[i] != -1) {
            res += num[i] * Math.pow(10, n - i -1);
          }
        }
      }
    }
    System.out.println(res);

  }
}

