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.*;

class Main{
  static int from(int n){
    if(n==1){
      return 0;
    }else if(n==2){
      return 10;
    }
    return 100;
  }
  static int to(int n){
    if(n==1){
      return 9;
    }else if(n==2){
      return 99;
    }
    return 999;
  }
  public static void main(String[] args){
    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()+'0';
    }
    for(int i=from(n);i<=to(n);i++){
      boolean flag=true;
      for(int j=0;j<m;j++){
        if(String.valueOf(i).charAt(s[j])!=c[j]){
          flag=false;
        }
      }
      if(flag){
        System.out.println(i);
        return;
      }
    }
    System.out.println(-1);
  }
}