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.Arrays;
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[] num =new int[N];
		Arrays.fill(num, -1);
		boolean ableFlg = true;

		if (N == 1 && M == 0) {
			System.out.print(0);
		}else if(N == 1 && M == 1){
			int insert = sc.nextInt();
			int number = sc.nextInt();
			System.out.println(number);
		}else {
			for (int i = 0; i < M; i++) {
				int insert = sc.nextInt();
				int number = sc.nextInt();

				if (insert == 1 && number == 0) {
					ableFlg = false;
					break;
				}

				if (num[insert - 1] != -1 && num[insert - 1] != number) {
					ableFlg = false;
					break;
				}

				num[insert - 1] = number;

			}

			if (ableFlg) {
				for (int i = 0; i < N; i++) {
					if (num[0] == -1) {
						num[0] = 1;
					}

					if (num[i] == -1) {
						System.out.print(0);
					}else {
						System.out.print(num[i]);
					}
				}
			}else {
				System.out.println(-1);
			}
		}
	}
}