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.*;

class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int ans = -1;
		int N = sc.nextInt();
		int M = sc.nextInt();
		boolean ok = true;
		
		int xxx[] = new int[3];
		
		for (int i=0; i<3; i++) {
			xxx[i] = -1;
		}
		
		for (int i=0; i<M; i++) {
			int s = sc.nextInt() - 1;
			int c = sc.nextInt();
			
			if (xxx[s] == -1) {
				xxx[s] = c;
			} else if (xxx[s] != c) {
				ok = false;
			}
		}
		
		if (xxx[0] == 0 && N > 1) {
			ok = false;
		} else if (xxx[0] == -1 && N > 1) {
			xxx[0] = 1;
		}
		
		if (ok) {
			for (int i=0; i<N; i++) {
				if (xxx[i] == -1) {
					xxx[i] = 0;
				} 
				System.out.print(xxx[i]);
			}
		} else {
			System.out.print(-1);
		}
	}
}