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();
		int M = sc.nextInt();

		int[] seisu = new int[N];
		for (int i=0; i<N; i++) {
			seisu[i] = -1;
		}
		
		boolean NG = false;
		
		for (int i=0; i<M; i++) {
			int s = sc.nextInt();
			int c = sc.nextInt();
			if (s > N) {
				NG = true;
				break;
			}
			else if (s == 1 && c == 0 && N != 1) {
				NG = true;
				break;
			}
			else if (seisu[s - 1] != -1 && seisu[s - 1] != c) {
				NG = true;
				break;
			}
			else {
				seisu[s - 1] = c;
			}
		}

		StringBuilder ans = new StringBuilder();
		if (NG) {
			ans.append(-1);
		}
		else {
			if (seisu[0] == -1) {
				seisu[0] = N == 1 ? 0 : 1;
			}
			
			for (int i = 0; i < N; i++) {
				ans.append(seisu[i] == -1 ? 0 : seisu[i]);
			}
		}
		
		System.out.println(ans);
	}
}