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);

        final int N = sc.nextInt();
        final int M = sc.nextInt();

        final int[][] p = new int[M][2];
        for (int i = 0; i < M; i++) {
            int s = sc.nextInt();
            int c = sc.nextInt();
            p[i][0] = s;
            p[i][1] = c;
        }

        for (int i = 0; i < 1000; i++) {
            String str = String.valueOf(i);
            if (str.length() != N) continue;

            boolean ok = true;
            for (int j = 0; j < M; j++) {
                int k = Character.getNumericValue(str.charAt(p[j][0]-1));
                if (k != p[j][1]) ok = false;
            }

            if (ok) {
                System.out.println(i);
                return;
            }
        }

        System.out.println(-1);
    }
}
