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();
        int kazu[] =new int[N+1];
        boolean flag = true;
        int ans = -1;
        for(int i=0;i<=N;i++){
            kazu[i]=-1;
        }
        for(int i=0;i<M;i++){
            int s = sc.nextInt();
            int c = sc.nextInt();
            if(kazu[s]!=-1 && kazu[s]!=c)flag=false;
            if(s==1 && c==0 && N!=1)flag = false;
            kazu[s] = c;
        }
        if(flag){
            String str="";
            for(int i=1;i<=N;i++){
                if(kazu[i]==-1){
                    kazu[i]=0;
                    if(i==1 && N!=1)kazu[i]=1;
                }
                str +=Integer.toString(kazu[i]);
            }
            ans=Integer.parseInt(str);
        }
        System.out.println(ans);
    }
}
