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 []result = new int[N];
        
        for (int i = 0; i < M; i++){
            int key = sc.nextInt();
            int value = sc.nextInt();
            
            if ((result[key-1] != 0 && result[key-1] != value) || (N >= 2 && key == 1 && value == 0)){
                System.out.println(-1);
                return;
            }
            result[key-1] = value; 
        }
            
        if (N >= 2 && result[0] == 0){
            result[0] = 1;
        }
        
        for (int i = 0; i < result.length; i++){
            System.out.print(result[i]);
        } 
        
    }
}
