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{

    Main(){
        Scanner SC = new Scanner(System.in);
        int N = Integer.parseInt(SC.next());
        int M = Integer.parseInt(SC.next());

        int[] R = new int[N];

        for(int i=0;i<N;i++){
            R[i] = -1;
        }

        for(int i=0;i<M;i++){
            int S = Integer.parseInt(SC.next());
            int C = Integer.parseInt(SC.next());

            if(R[S-1] == -1){
                R[S-1] = C;
            } else {
                if(R[S-1] != C){
                    System.out.println(-1);
                    return;
                }
            }
        }

        if(N == 1){
            if(R[0] == -1){
                R[0] = 0;
            }
        } else {
            if(R[0] == 0){
                System.out.println(-1);
                return;
            } else if(R[0] == -1){
                R[0] = 1;
            }

            for(int i=1;i<N;i++){
                if(R[i] == -1){
                    R[i] = 0;
                }
            }
        }

        for(int i=0;i<N;i++){
            System.out.print(R[i]);
        }
        System.out.println("");
    }

    public static void main(String[] args){
        Main main = new Main();
    }
}
