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 sc=new Scanner(System.in);
        long o=0;
        int n=sc.nextInt();
        int m=sc.nextInt();
        long[] x=new long[n];
        boolean[] id=new boolean[n];
      for(int i=0;i<m;i++){
        int s=sc.nextInt()-1;
        int c=sc.nextInt();
      	if(id[s]&&x[s]!=c){
          o=-1;
          break;
        }else{
          id[s]=true;
          x[s]=c;  
        }                
      }
      if(n>1&&id[0]&&x[0]==0)o=-1;
      if(o>=0){
        for(int i=0;i<n;i++){
              o*=10;
              if(id[i]){
                  o+=x[i];
              }else if(i==0&&n>1){
                  o++;
              }
          }
      }
      System.out.println(o);
    }
    
}