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{
  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();
      c[i]=sc.nextInt();
    }
    for(int i=0;i<1000;i++){
      String str=String.valueOf(i);
      if(str.length()==n){
        boolean flag=true;
        for(int j=0;j<m;j++){
          flag=flag&&(str.charAt(s[j]-1)==c[j]+'0');
        }
        if(flag){
          System.out.println(i);
          return;
        }
      }
    }
    System.out.println(-1);
  }
}
