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[] a=new int[n];
    Arrays.fill(a,-1);
    for(int i=0;i<m;i++){
      int s=sc.nextInt();
      int c=sc.nextInt();
      if(a[s-1]!=-1&&a[s-1]!=c){
        System.out.println(-1);
        return;
      }else{
        a[s-1]=c;
      }
    }
    if(n==1){
      if(a[0]==-1){
        a[0]=0;
      }
      System.out.println(a[0]);
    }else{
      if(a[0]==0){
        System.out.println(-1);
        return;
      }
      if(a[0]==-1){
        a[0]=1;
      }
      if(n>1&&a[1]==-1){
        a[1]=0;
      }
      if(n>2&&a[2]==-1){
        a[2]=0;
      }
      int ans=0;
      for(int i=0;i<n;i++){
        ans*=10;
        ans+=a[i];
      }
      System.out.println(ans);
    }
  }
}