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) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();
        int[] z = new int[N];

        for (int i = 0; i < M; i++){
            int a = sc.nextInt();
            int b = sc.nextInt();

            if ((z[a-1] != 0 && z[a-1] != b) || (N >= 2 && a == 1 && b == 0)){
                System.out.println(-1);
                return;
            }
            z[a-1] = b;
        }

        if (N >= 2 && z[0] == 0){
            z[0] = 1;
        }

        for (int i = 0; i < z.length; i++){
            System.out.print(z[i]);
        }

    }
}