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=sc.nextInt(),m=sc.nextInt(),s=0,buff=-1;
		int[] c = new int[5];
		for(int i=0;i<5;i++) {
			c[i]=-1;
		};
		for(int i=0;i<m;i++) {
			s=sc.nextInt();
			buff=sc.nextInt();
			if(c[s-1]!=-1&&c[s-1]!=buff) {
				System.out.println(-1);
				System.exit(0);
			}
			c[s-1]=buff;
		}
		StringBuilder res= new StringBuilder();
		if(c[0]==0 && n!=1) {
			System.out.println(-1);
			System.exit(0);
		}
		for(int i=0;i<n;i++) {
			if(c[i]==-1&&i==0&&n!=1) {
				res.append("1");
			}else if(c[i]==-1) {
				res.append(0);
			}else {
				res.append(c[i]);
			}
		}
		System.out.println(res.toString());
	}
}

