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) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int m = sc.nextInt();

		boolean edit[] = new boolean[n];

		String num = "1";
		if(n == 1){
			num = "0";
		}

		for(int i = 1; i < n; i++){
			num += 0;
		}
		for(int i = 0; i < m; i++){
			int s = sc.nextInt() - 1;
			int c = sc.nextInt();

//			System.out.println(s + " "+ c);
			if(edit[s] && num.charAt(s) != '0' + c){
				System.out.println(-1);
				return;
			}

			if(n >= 2 && s == 0 && c == 0){
				System.out.println(-1);
				return;
			}
			edit[s] = true;
			num = num.substring(0, s) + c + num.substring(s + 1, n);
		}

		System.out.println(num);
	}

}
