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[]) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        int[] arr = new int[n];
       	Arrays.fill(arr, -1);
        while(m-- > 0) {
        	int idx = sc.nextInt() - 1;
        	int num = sc.nextInt();
        	if(n > 1 && idx == 0 && num == 0 || arr[idx] > -1 && arr[idx] != num) {
        		System.out.println(-1);
        		return;
        	}
        	arr[idx] = num;
        }
        if(n == 1 && arr[0] == -1) {
            System.out.println(0);
            return;
        }
        for(int i = 0; i < n; i++) {
        	if(i == 0 && arr[i] == -1) {
        		System.out.print(1);
        		continue;
        	} 
        	if(arr[i] == -1)
        		System.out.print(0);
        	else
        		System.out.print(arr[i]);
        }
        System.out.println();
    }
}
