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.Scanner;

public class Main {

	static int min;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int M = sc.nextInt();
		int[] s = new int[M];
		int[] c = new int[M];
		for(int i = 0;i < M;i++){
			s[i] = sc.nextInt();
			c[i] = sc.nextInt();
		}
		sc.close();
		if(N==1){
			min = 0;
		}else{
			min = (int)Math.pow(10, N-1);
		}
		for(int i = min;i < (int)Math.pow(10, N);i++){
			String str = String.valueOf(i);
			boolean b = true;
			for(int j = 0;j < M;j++){
				if(!str.substring(s[j]-1,s[j]).equals(String.valueOf(c[j]))){
					b = false;
					break;
				}
			}
			if(b){
				System.out.println(i);
				return;
			}
		}
		System.out.println(-1);
	}
}