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) throws Exception {
      
        Scanner sc = new Scanner(System.in);
        int n,m;
        n=sc.nextInt();
        m=sc.nextInt();
        int[] s=new int[m];
        int[] c=new int[m];
        for(int i=0;i<m;i++){
            s[i]=sc.nextInt();
            c[i]=sc.nextInt();
        }
      
        System.out.println(solve(n,m,s,c));
    }

    public static String solve(int n,int m,int[] s,int[] c){
        for(int i=0;i<1000;i++){
            String str=String.valueOf(i);
            if(ok(str,n,m,s,c)){
                return str;
            }
        }
        return "-1";
    }

    public static Boolean ok(String str,int n,int m,int[] s,int[] c){
        if(n!=str.length()) return false;
        for(int i=0;i<m;i++){
            if(str.charAt(s[i]-1)!=c[i]+'0') return false;
        }
        return true;
    }
}