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.Arrays;
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();
		int x[] = new int[n];
		Arrays.fill(x, -1);

		boolean can = true;
		for (int i = 0; i < m; i++) {
			int s = sc.nextInt();
			int c = sc.nextInt();
			if (x[s - 1] != -1 && x[s - 1] != c) can = false;
			x[s - 1] = c;
		}

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

		if (x[0] == 0 || !can) {
			System.out.println(-1);
		} else if (x[0] == -1) {
			x[0] = 1;
			System.out.println(Arrays.toString(x).replace("-1", "0").replace("[", "").replace("]", "").replace(", ", ""));
		} else {
			System.out.println(Arrays.toString(x).replace("-1", "0").replace("[", "").replace("]", "").replace(", ", ""));
		}

		sc.close();

	}

}