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