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 in=new Scanner(System.in);
		int flag=0;
		int n=in.nextInt();
		int m=in.nextInt();
		int c1=77,c2=77,c3=77;
		if(m==0&&n==1) System.out.print(0);
		else if(m==0&&n==2) System.out.print(10);
		else if(m==0&&n==3) System.out.print(100);
		else if(n==1)
		{
			for(int i=0;i<m;i++)
			{
				int s=in.nextInt();
				int c=in.nextInt();
				if((s==1&&c1==77)||(s==1&&c==c1)) c1=c;
				else flag=1;
			}
			if(flag==1) System.out.print(-1);
			else System.out.print(c1);
		}
		else
		{
			for(int i=0;i<m;i++)
			{
				int s=in.nextInt();
				int c=in.nextInt();
				if((s==1&&c1==77)||(s==1&&c==c1))
				{
					if(c==0) flag=1;
					else c1=c;
				}
				else if((s==2&&c2==77)||(s==2&&c==c2)) c2=c;
				else if((s==3&&c3==77)||(s==3&&c==c3)) c3=c;
				else flag=1;
			}
			if(flag==1) System.out.print(-1);
			else
			{
				for(int i=1;i<=n;i++)
			{
					if(i==1&&c1!=77) System.out.print(c1);
					if(i==1&&c1==77) System.out.print(1);
					if(i==2&&c2!=77) System.out.print(c2);
					if(i==2&&c2==77) System.out.print(0);
					if(i==3&&c3!=77) System.out.print(c3);
					if(i==3&&c3==77) System.out.print(0);
			    }
			}
		}
        in.close();
	}
}