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)throws Exception{
		Scanner stdIn=new Scanner(System.in);
		int N=stdIn.nextInt();
		int M=stdIn.nextInt();
		int S[]=new int[N];
		boolean key[]=new boolean[N];
		String ans="";
		for(int i=0;i<M;i++){
			int s=stdIn.nextInt()-1;
			int c=stdIn.nextInt();
			if(s==0&&c==0&&N>1){
				System.out.println(-1);
				System.exit(0);
			}
			if(key[s]&&S[s]!=c){
				System.out.println(-1);
				System.exit(0);
			}
			else{
				key[s]=true;
				S[s]=c;
			}
		}
		for(int i=0;i<N;i++){
			if(i==0&&S[i]==0&&key[i]==false&&N!=1){
				S[i]=1;
			}
			ans+=String.valueOf(S[i]);
		}
		System.out.println(ans);
	}
}
