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 void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int n = scan.nextInt();
		int m = scan.nextInt();
		int[] s = new int[m];
		int[] c = new int[m];

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


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


			String g = String.valueOf(i);
			boolean flg = true;


			if(g.length() != n) {
				flg = false;
			}


			for(int j=0;j<m;j++) {

				if(g.length() < s[j]) {
					flg = false;
				}else {
				if(Integer.valueOf(g.substring(s[j]-1,s[j])) != c[j]) {
					flg = false;
				}
			}
		}

		if(flg) {
			System.out.println(i);
			return;
		}
		}
		System.out.println(-1);

		scan.close();

	}

}
