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.Scanner;
 
public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int m = sc.nextInt();
    int num[] = new int[n];
    for(int i = 0; i < n; i++){
      num[i] = -1;
    }
    for(int i = 0; i < m; i++){
      int s = sc.nextInt()-1;
      int c = sc.nextInt();
      if((s==0&&c==0&&n!=1)||(num[s] != -1&&num[s] != c)){
        System.out.println(-1);
        return;
      } else {
        num[s] = c;
      }
    }
    int ans = 0;
    int ten = 1;
    for(int i = n-1; i >= 0; i--){   
      if(num[i]==-1){
        if(n>1&&i==0){
          num[i]=1;
        } else {
          num[i]=0;
        }
      }
      ans += num[i]*ten;
      ten*=10;
    }
    System.out.println(ans);
  }
}