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 scn = new Scanner(System.in);

    int N = scn.nextInt(), M = scn.nextInt();
    int s[] = new int[M], c[] = new int[M];
    for (int i = 0; i < M; i++) {
      s[i] = scn.nextInt();
      c[i] = scn.nextInt();
    }

    int ans = -1;
    int t = (N != 1 ? (int) Math.pow(10, N - 1) : 0);
    for (int i = t; i < (int) Math.pow(10, N); i++) {
      Boolean flag = true;
      for (int j = 0; j < M; j++) {
        if (N < j) {
          flag = false;
          break;
        }
        String str = String.valueOf(i);
        String C = String.valueOf(c[j]);
        if (!str.substring(s[j] - 1, s[j]).equals(C)) {
          flag = false;
          break;
        }
      }
      if (flag) {
        ans = i;
        break;
      }
    }

    System.out.println(ans);
  }
}
