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[] a = new int[n];Arrays.fill(a, -1);
		boolean flag = true;
		for (int i = 0; i < m; i++) {
			int s = sc.nextInt()-1;
			if(a[s]==-1)a[s] = sc.nextInt();
			else {
				if(a[s] == sc.nextInt())continue;
				else flag = false;
			}
		}
		if(!flag)System.out.println(-1);
		else if(n==1) {
			if(a[0]==-1)System.out.println(0);
			else System.out.println(a[0]);
		}else if(a[0]==0) {
			System.out.println(-1);
		}else {
			for (int i = 0; i < n; i++) {
				if(a[i]!=-1)System.out.print(a[i]);
				else{
					if(i!=0)System.out.print(0);
					else System.out.print(1);
				}
			}
		}
		sc.close();
	}
}