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) throws Exception {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt();
        int M = in.nextInt();
        P[] Ps = new P[M];

        for (int m = 0; m < M; m++) {
            P p = new P();
            p.s = in.nextInt();
            p.c = in.nextInt();
            Ps[m] = p;
        }

        int first = 0;
        if (N > 1) {
            first = (int) Math.pow(10, N - 1);
        }

        for (int i = first; i < Math.pow(10, N); i++) {
            boolean b = true;
            for (P p : Ps) {
                if (get(i, p.s) != p.c) {
                    b = false;
                    break;
                }
            }

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

        System.out.println(-1);
    }

    private static int get(int a, int s) {
        String as = Integer.toString(a);
        return Integer.parseInt(as.substring(s - 1, s));
    }
}

class P {
    public int s;
    public int c;
}