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.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt(), m = scan.nextInt();
        int[] num = new int[n];
        boolean[] found = new boolean[n];
        //int min = Integer.MAX_VALUE;
        for (int i = 0; i < m; i ++){
            int a = scan.nextInt(), b = scan.nextInt();
            if (found[a - 1]){
                if (num[a - 1] != b){
                    System.out.println("-1");
                    return;
                }
            }
            else{
                found[a - 1] = true;
                num[a - 1] = b;
            }
        }
        if (num[0] == 0 && n != 1 && found[0]){
            System.out.println("-1");
            return;
        }
        if (num[0] == 0 && n != 1){
            num[0] = 1;
        }
        for (int i : num)
            System.out.print(i);
        

    }
}
