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(),M=sc.nextInt();
		int[][] q = new int[M][2];
		for (int i=0;i<M;i++) {
			q[i][0]=sc.nextInt();
			q[i][1]=sc.nextInt();
		}
		boolean flag = true;
		for (int i=0;i<M;i++) {
			if (N!=1&&q[i][0]==1&&q[i][1]==0) {
				flag = false;
			}
		}
		
		for (int i=0;i<M-1;i++) {
			for (int j=i+1;j<M;j++) {
				if(q[i][0]==q[j][0] && q[i][1]!=q[j][1]) {
					flag = false;
				}
				if(q[i][0]==q[j][0] && q[i][1]==q[j][1]) {
					q[j][0]=0;
				}
			}
		}
		int ans= 0;
		if(flag) {
			for (int i=0;i<M;i++) {
				if (q[i][0]!=0) {
					ans+= q[i][1]*(int)Math.pow(10, N-q[i][0]);
				}
			}
			if(N==3&& ans<100) {
				ans+=100;
			}else if(N==2&& ans<10){
				ans+=10;
			}
			System.out.println(ans);
		}else {
			System.out.println(-1);
		}
		
	}

}