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 s[] = new int[M];
		int c[] = new int[M];
		
		for(int i = 0; i < M; i++){
			s[i] = sc.nextInt() - 1;
			c[i] = sc.nextInt();
		}
		
		int ans = -1;
		for(int n = (N == 1)?0:(int)Math.pow(10, N-1); n < (int)Math.pow(10, N); n++){
			String str = String.valueOf(n);
			boolean flag = false;
			for(int j = 0; j < M; j++){
				if(str.charAt(s[j])-'0' != c[j]){
					flag = true;
					break;
				}
			}
			if(flag)continue;
			else {
				ans = n;
				break;
			}
		}
		
		System.out.println(ans);
	}
}