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[] s = new int[m];
		int[] c = new int[m];

		for (int i = 0; i < m; i++) {
			s[i] = sc.nextInt();
			c[i] = sc.nextInt();
		}

		int[] ans = new int[n];
		Arrays.fill(ans, -1);
		//s,cの値を代入していく。コンフリクトが発生したらfalse.
		for (int i = 0; i < m; i++) {
			if (ans[s[i] - 1] != -1 && ans[s[i] - 1] != c[i]) {
				System.out.println(-1);
				return;
			}
			ans[s[i] - 1] = c[i];
		}

		boolean flag = true;
		for (int i = 0; i < n; i++) {
			if (flag && ans[i] == 0 && i != n - 1) {
				System.out.println(-1);
				return;
			} else if (flag && ans[i] == -1 && i == n - 1) {
				System.out.print(0);
				flag = false;
			} else if (flag && ans[i] == -1) {
				System.out.print(1);
				flag = false;
			} else if (!flag && ans[i] == -1) {
				System.out.print(0);
			} else {
				System.out.print(ans[i]);
				flag = false;
			}
		}

	}

}
