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 scan = new Scanner(System.in);
        int n = scan.nextInt();
        int m = scan.nextInt();
        if(n == 1 && m == 0){
            System.out.println(0);
            return;
        }
        int[] s = new int[m];
        int[] c = new int[m];
        int[] out = new int[n];
        for(int i = 0; i < m; i++){
            s[i] = scan.nextInt();
            c[i] = scan.nextInt();
        }
        out[0] = 1;
        boolean[] isExist = new boolean[n];
        Arrays.fill(isExist, true);
        for(int i = 0; i < m; i++){
            if(isExist[s[i] - 1] || out[s[i] - 1] == c[i]) {
                out[s[i] - 1] = c[i];
                isExist[s[i] - 1] = false;
            }else{
                System.out.println(-1);
                return;
            }
        }
        if(out[0] == 0 && n != 1){
            System.out.println(-1);
            return;
        }
        for(int i = 0; i < n; i++) System.out.print(out[i]);
        scan.close();
    }
}
