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){
      //入力値の取得
      Scanner sc = new Scanner(System.in);
      int n = sc.nextInt();
      int m = sc.nextInt();
      int[][] array = new int[m][2];
	  for (int i=0; i < m; i++) {
		  sc.nextLine();
		  array[i][0] = sc.nextInt();
		  array[i][1] = sc.nextInt();
	  }
	  sc.close();
 
	  //検査対象整数
	  int min=(int) Math.pow(10, n-1);
	  if (n==1) {
		  min=0;
	  }
	  int max=(int) Math.pow(10, n)-1;
 
	  int answer=-1;
	  outer: for(int i=min; i<=max; i++) {
		  char[] target = Integer.toString(i).toCharArray();
          if (m==0) {
            answer=i;
            break;
          }
		  for(int j=0; j<m; j++) {
			  if (!String.valueOf(target[array[j][0]-1]).equals(Integer.toString(array[j][1]))) {
				  break;
			  }
			  if (j==m-1) {
				  answer=i;
				  break outer;
			  }
		  }
	  }
	  System.out.println(answer);
  	}
}