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 in = new Scanner(System.in);
        int n = in.nextInt()-1;
        int m = in.nextInt();
        int[] s = new int[m];
        String[] c = new String[m];
        for(int i=0; i<m; i++) {
            s[i] = in.nextInt();
            c[i] = in.next();
        }
        int start = (int)Math.round(Math.pow(10, n));
        int end = start*10;
        if(start==1) {
            start = 0;
        }

        for(int i=start; i<end; i++) {
            String str = Integer.toString(i);
            boolean isOK = true;
            for(int j=0; j<m; j++) {
                if(!str.substring(s[j]-1, s[j]).equals(c[j])) {
                    isOK = false;
                    break;
                }
            }
            if(isOK) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}
