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) throws Exception {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int m = in.nextInt();

        int[] s = new int[m];
        int[] c = new int[m];
        for (int i = 0; i < m; i++) {
            s[i] = in.nextInt();
            c[i] = in.nextInt();
        }
        int limit = 1;
        for (int i = 0; i < n; i++) {
            limit *= 10;
        }
        for (int i = 0; i < limit; i++) {
            String is = String.valueOf(i);
            if (is.length() != n) {
                continue;
            }
            boolean ok = true;
            for (int j = 0; j < m; j++) {
                if (is.charAt(s[j] - 1) != c[j] + 48) {
                    ok = false;
                    break;
                }
            }
            if (ok) {
                System.out.println(i);
                return;
            }
        }
        System.out.println(-1);
    }
}
