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();

		String[] temp = new String[N];
		for (int i = 0; i < M; i++) {

			int s = sc.nextInt();
			int c = sc.nextInt();

			if(temp[s-1] != null && Integer.parseInt(temp[s-1]) != c) {
				System.out.println(-1);
				return;
			}
			temp[s-1] = String.valueOf(c);
		}

//		if(M==0) {
//			if(N==1) {
//				System.out.println(0);
//			} else {
//				System.out.println(-1);
//			}
//			return;
//		}

		if(temp[0] != null && N>=2 && Integer.parseInt(temp[0]) == 0) {
			System.out.println(-1);
			return;
		}

		StringBuilder result = new StringBuilder();

		for (int i = 0; i < N; i++) {

			if(i == 0 && temp[0] == null && N != 1) {
				result.append("1");
				continue;
			}

			if(temp[i] != null) {
				result.append(temp[i]);
			} else {
				result.append("0");
			}
		}

		int resultInt = Integer.parseInt(result.toString());
		if(N ==1 && resultInt == 0) {
			System.out.println(0);
			return;
		}

		if((int)Math.pow(10, N-1) <= resultInt && (int)Math.pow(10, N) > resultInt) {
			System.out.println(Integer.parseInt(result.toString()));
		} else {
			System.out.println(-1);
		}
	}
}