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.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		List<Obj> list = new ArrayList<>();
		for (int i = 0; i < m; i++) {
			list.add(new Obj(sc.nextInt(), sc.nextInt()));
		}

		int max = (int) Math.pow(10, n) - 1;
		for (int i = 0; i <= max; i++) {
			int num = i;

			if (Integer.toString(i).length() != n) {
				continue;
			}

			int[] nums = new int[n];
			for (int j = 0; j < n; j++) {
				nums[n - j - 1] = num % 10;
				num = num / 10;
			}

			boolean temp = true;
			for (Obj o : list) {
				temp = temp && nums[o.k - 1] == o.v;
			}
			if (temp) {
				System.out.println(i);
				return;
			}
		}
		System.out.println(-1);
	}

	private static class Obj {
		public Integer k;
		public Integer v;

		public Obj(Integer k, Integer v) {
			this.k = k;
			this.v = v;
		}
	}
}
