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.*;

class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();//ヒント
        int[] s = new int[m];
        int[] c = new int[m];
        int[] ans = new int[n];
        Arrays.fill(ans,-1);
        int range = (int)Math.pow(10,n);
        for(int i = 0;i < m;i++){
            s[i] = sc.nextInt()-1;
            c[i] = sc.nextInt();
        }
            
        for(int i = 0;i <= range;i++){
            String str = String.valueOf(i);
            if(str.length()==n){
                boolean flag = true;
                for(int j=0;j<m;j++){
                    flag = flag&&(str.charAt(s[j])==c[j]+'0');
                }
                if(flag){
                    System.out.println(i);
                    return;
                }
            }
        }
        System.out.println(-1);
    }
}