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 sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		int[] r = new int[n];
		int[] s = new int[m];
		int[] c = new int[m];
		boolean[] flag = new boolean[n];
		for(int i = 0; i < m; i++) {
			s[i] = sc.nextInt();
			c[i] = sc.nextInt();
			if(!flag[s[i]-1]) {
				r[s[i]-1] = c[i];
				flag[s[i]-1] = true;
			}else if(r[s[i]-1] != c[i]) {
				System.out.println("-1");
				System.exit(0);
			}
			if(n != 1 && s[i] == 1 && c[i] == 0) {
				System.out.println("-1");
				System.exit(0);
			}
		}
		if(!flag[0])r[0] = 1;
		if(n==1 && !flag[0])r[0] = 0;
		for(int i = 0; i < n; i++) {
			System.out.print(r[i]);
		}
		System.out.println();
	}

}
