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();
        sc.nextLine();

        int[] ans = new int[N];

        for (int i = 0; i < M; i++) {
            int p = sc.nextInt() - 1;
            int a = sc.nextInt();

            if (ans[p] != a && ans[p] != 0) {
                System.out.println(-1);
                System.exit(0);
            }
            
            ans[p] = a;
                
            if (p == 0 && a == 0 && N != 1) {
                System.out.println(-1);
                System.exit(0);
            }
            sc.nextLine();
        }

        int s = 1;
        int a = 0;
        if (ans[0] == 0 && N != 1) { ans[0] = 1; }

        for (int i = N-1; i >= 0; i--) {
            a += ans[i] * s;
            s *= 10;
        }

        System.out.println(a);
    }
}