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.*;
public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int M = sc.nextInt();
		if(M == 0) {
			if(N == 1)
				System.out.println(0);
			else if(N == 2)
				System.out.println(10);
			else
				System.out.println(100);
			return;
		}
		int[] ans = new int[N];
		boolean[] used = new boolean[N];
		for(int i = 0; i < M; i++) {
			int s = sc.nextInt();
			int c = sc.nextInt();
			if(used[s-1] && ans[s-1] != c) {
				System.out.println(-1);
				return;
			}
			ans[s-1] = c;
			used[s-1] = true;
		}
		if(used[0] && ans[0] == 0) {
			if(N == 1)
				System.out.println(0);
			else
				System.out.println(-1);
			return;
		}
		else if(ans[0] == 0)
			ans[0] = 1;
		for(int i = 0; i < N; i++)
			System.out.print(ans[i]);

	}

}