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.*;

public class Main{
	public static void main(String[] $){
		Scanner s=new Scanner(System.in);
		int n=s.nextInt();
		int[] d=new int[n];
		Arrays.fill(d,-1);
		for(int m=s.nextInt();m>0;--m){
			int e=s.nextInt()-1;
			int c=s.nextInt();
			if(n>1&&e+c==0||d[e]>0&&d[e]!=c){
				System.out.println(-1);
				return;
			}
			d[e]=c;
		}
		for(int i=0;i<n;++i)
			if(d[i]<0)
				d[i]=i<1&&n>1?1:0;
		System.out.println(Arrays.toString(d).replaceAll("\\D",""));
	}
}
