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 {
	Scanner sc;
	int N, M;
	
	private void calc() {
		sc = new Scanner(System.in);
		N = sc.nextInt();
		M = sc.nextInt();
		int[] s = new int[M];
		int[] c = new int[M];
		for (int i = 0; i < M; i++) {
			s[i] = sc.nextInt();
			c[i] = sc.nextInt();
		}
		int i = 0;
	lp:
		for (; i < 1000; i++) {
			String n = String.valueOf(i);
			if (n.length() != N) continue;
			for (int j = 0; j < M; j++) {
				if ( (n.charAt(s[j]-1) - '0') != c[j]) continue lp;
			}
			break;
		}
		if (i == 1000) System.out.println(-1);
		else System.out.println(i);
	}

	public static void main(String[] args) {
		new Main().calc();
	}
}
