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();

		if(n==1&&m==0) {
			System.out.println("0");
			return;
		}

		int[] c = new int[n+1];
		for(int i=0;i<n+1;i++) {
			c[i] = -1;
		}
		int s1,s2;
		for(int i=0; i<m;i++) {
			s1 = sc.nextInt();
			s2 = sc.nextInt();
			if(c[s1]==-1) {
				c[s1] = s2;
				continue;
			}
			if(c[s1] == s2) {
				continue;
			}
			System.out.println("-1");
			return;
		}


		if(c[1] == 0) {
			if(n==1) {
				System.out.println("0");
				return;
			}
			System.out.println("-1");
			return;
		}

		int ans = 0;
		for(int i=1;i<n+1;i++) {
			if(c[i]==-1) {
				if(i==1) {
					ans += 1 * Math.pow(10, n-i);
				}
			}else {
				ans += c[i] * Math.pow(10, n-i);
			}

		}

		System.out.println(ans);
	}

}
