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;
import java.util.Arrays;
public class Main{
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		int a[] = new int[n];Arrays.fill(a,-1);
		boolean f = false;
		for(int i=0;i<m;i++){
			int s = sc.nextInt()-1;
			int c = sc.nextInt();
			if(a[s]==-1||a[s]==c){
				a[s]=c;
			}else{
				f=true;
			}
		}


		if(m==0){
			if(n==1){
				a[0]=0;
			}else{
				a[0]=1;
			}
		}

		if(a[0]==0&&n>1)f=true;

		if(a[0]==-1){
			if(n>1){
				a[0]=1;
			}else{
				a[0]=0;
			}
		}


		if(!f){
			for(int i:a){
				int an = i == -1 ? 0 : i;
				System.out.print(an);
			}
			System.out.println();
		}else{
			System.out.println(-1);
		}
	}
}
