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.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int M = sc.nextInt();
        int[] a = new int[N + 1];
        int[] b = new int[N + 1];
        for (int i = 0; i < M; i++) {
            int s = sc.nextInt();
            int c = sc.nextInt();
            if (N > 1 && s == 1 && c == 0) {
                System.out.print("-1");
                return;
            }
            if (b[s] == 0) {
                a[s] = c;
                b[s]++;
            } else {
                if (a[s] != c) {
                    System.out.print("-1");
                    return;
                }
            }
        }

        if (N == 1 && b[1] == 0) {
            System.out.println("0");
            return;
        }
        for (int i = 1; i < N + 1; i++) {
            if (b[i] == 0 && i == 1) {
                a[i] = 1;
            }
            System.out.print(a[i]);
        }
    }
}
