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.io.*;
import java.util.*;

public class Main{
    public static void main(String[] args)throws Exception{
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt(),m=sc.nextInt();
        int[] ary=new int[n];
        Arrays.fill(ary,-1);
        boolean flag=true;
        for(int i=0;i<m;i++){
            int s=sc.nextInt();
            int c=sc.nextInt();
            if(ary[s-1]>-1&&ary[s-1]!=c){
                flag=false;
            }else{
                ary[s-1]=c;
            }
        }
        if(!flag||(ary[0]==0&&n!=1)){
            System.out.println(-1);
        }else if(n==1){
            if(ary[0]==-1){
                System.out.println(0);
            }else{
                System.out.println(ary[0]);
            }
        }else{
            for(int i=0;i<n;i++){
                if(ary[i]==-1){
                    if(i==0){
                        System.out.print(1);
                    }else{
                        System.out.print(0);
                    }
                }else{
                    System.out.print(ary[i]);
                }
            }
            System.out.println();
        }
    }
}