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){
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();
    int m = scan.nextInt();

    boolean [] a = new boolean[n];
    int [] g = new int[n];
    for (int t = 0;t<n;t++){
      a[t] = true;
      g[t] = 0;
    }

    for (int i=0; i<m; i++){
      int b = scan.nextInt();
      if (a[b-1] == false){
        int gg = scan.nextInt();
        if (gg != g[b-1]){
          System.out.println(-1);
          return;
        }
      }
      else{
        a[b-1] = false;
        int c = scan.nextInt();
        g[b-1] = c;
        if ((c == 0)&&(b == 1)&&(n != 1)){
          System.out.println(-1);
          return;
        }
      }
    }

    if ((g[0] == 0) && (n == 1)){
      System.out.println(0);
      return;
    }

    if (g[0] == 0){
      g[0] = 1;
    }

    for (int t = 0;t<n;t++){
      System.out.print(g[t]);
    }
    System.out.println("");
  }
}
