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();
        int[] p = new int[n];
        for(int i=0;i<n;i++){
            p[i]=-1;
        }
        for(int i=0;i<m;i++){
            int s = sc.nextInt();
            int c = sc.nextInt();
            if(p[s-1]==-1){
                p[s-1]=c;
            }
            else{
                if(p[s-1]==c)continue;
                System.out.println(-1);
                return;
            }
        }


        if(p[0]==-1){
            if(n==1){
                System.out.print(0);
            }
            else{
                System.out.print(1);
            }
        }
        else if(p[0]==0){
            if(n==1){
                System.out.println(0);
                return;
            }
            System.out.print(-1);
            return;
        }
        else {
            System.out.print(p[0]);
        }
        for(int i=1;i<n;i++){
            if(p[i]==-1){
                System.out.print(0);
            }
            else{
                System.out.print(p[i]);
            }
        }

    }
}
