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.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();

        Map<Integer, Integer> map = new HashMap<>();

        for (int i=0; i<m; i++) {
            int keta = sc.nextInt();
            int num = sc.nextInt();

            if (keta == 1 && num == 0 && n >= 2) {
                System.out.println(-1);
                return;
            }

            if (map.containsKey(keta)) {
                if (!map.get(keta).equals(num)) {
                    System.out.println(-1);
                    return;
                }
            }

            map.put(keta, num);
        }

        StringBuilder sb = new StringBuilder();
        for (int i=1; i<=n; i++) {
            if (map.containsKey(i)) {
                sb.append(map.get(i));
            } else {
                if (i == 1 && n >= 2) {
                    sb.append(1);
                } else {
                    sb.append(0);
                }
            }
        }

        System.out.println(sb.toString());
    }
}
