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.Scanner;

public class Main {

	public static int N;
	public static int M;
	public static int[] S;
	public static int[] C;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		N = sc.nextInt();
		M = sc.nextInt();
		S = new int[M];
		C = new int[M];
		for (int i = 0; i < M; i++) {
			S[i] = sc.nextInt() - 1;
			C[i] = sc.nextInt();
		}
		System.out.println(solve());
	}

	public static boolean ok(String x) {
		if (x.length() != N) {
			return false;
		}
		for (int i = 0; i < M; i++) {
			int s = Integer.valueOf(x.substring(S[i], S[i] + 1));
			if (s != C[i]) {
				return false;
			}
		}
		return true;
	}

	public static String solve() {
		for (int i = 0; i < 1000; i++) {
			String x = String.valueOf(i);
			if (ok(x)) {
				return x;
			}
		}
		return "-1";
	}

}