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.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		
		int[] v = new int[n];
		Arrays.fill(v, -1);
		
		for (int i = 0; i < m; i++) {
			int s = sc.nextInt() - 1;
			int c = sc.nextInt();
			
			if (v[s] != -1 && v[s] != c) {
				System.out.println(-1);
				sc.close();
				return;
			}
			
			v[s] = c;
		}
		
		if (n > 1 && v[0] == 0) {
			System.out.println(-1);
			sc.close();
			return;
		}
		
		for (int i = 0; i < v.length; i++) {
			System.out.print(v[i] > 0 ? v[i] : (i == 0 ? (n == 1 ? 0 : 1) : 0));
		}
		System.out.println();
	}

}
