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) {
        // write your code here

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        int[] list = new int[n];
        Arrays.fill(list, - 1);
        for (int i = 0; i < m; i++) {
            int orderIndex = sc.nextInt();
            int v = sc.nextInt();
            if (list[orderIndex - 1] >= 0 && list[orderIndex - 1] != v) {
                System.out.println(-1);
                return;
            }
            list[orderIndex -1] = v;
        }

        if (n > 1 && list[0] == 0) {
            System.out.println(-1);
            return;
        }

        if (list[0] == -1) {
            if (n == 1) {
                list[0] = 0;
            } else {
                list[0] = 1;
            }
        }

        StringBuilder builder = new StringBuilder();
        for (Integer v: list
             ) {
            if (v == - 1) {
                v = 0;
            }
            builder.append(v);
        }
        int ans = Integer.parseInt(builder.toString());
        System.out.println(ans);
    }
}