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 {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N,M;
		N= sc.nextInt();
		M= sc.nextInt();
		int a[],b[];
		a = new int[3];
		b = new int[3];
		a[0] = a[1]=a[2]=0;
		b[0] = b[1]=b[2]=0;
		for (int i =0;i<M;i++) {
			int s,c ;
			s= sc.nextInt();
			c= sc.nextInt();
			if (s==1&&c==0&&N>1) {
				System.out.println("-1");
				return ;
			}
			if (a[s-1]==0 && b[s-1]==0) {
				a[s-1] =c;
			}else if (a[s-1]==0 && b[s-1]>0) {
				if (c!=0) {
					System.out.println("-1");
					return ;
				}
			}else {
				if (a[s-1] !=c) {
					System.out.println("-1");
					return ;
				}

			}
			b[s-1]++;
		}
		if (N>1 && a[0]==0) {
			a[0]=1;
		}
		for (int i=0;i<N;i++) {
			System.out.print(a[i]);
		}
	}
}