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[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		boolean col=true;
		int[] preAns=new int[n];
		preAns[0]=1;				
		boolean[] PAalre=new boolean[n];

		int s;
		int c;
		for(int i=0;i<m;i++){
			s= sc.nextInt()-1;
			c= sc.nextInt();
				if(PAalre[s]){
					if(c!=preAns[s]){
						col=false;
					}
				}else{
					PAalre[s]=true;
					preAns[s]=c;
				}	
		}
		if(preAns[0]==0&&n!=1){
			col=false;
		}
      	if(m==0&&n==1){
          preAns[0]=0;
        }
		if(col){
			String ans="";
			for(int i=0;i<n;i++){
				ans=ans+preAns[i];
			}
			System.out.println(ans);
		}else{
			System.out.println(-1);
		}
	}
}