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.*;
import java.lang.*;
public class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int M = sc.nextInt();
		int[] D = new int[4];
		int[] point = new int[4];
		int ans = 0;
		for( int i=0; i<M; i++ ){
			int a = sc.nextInt();
			int b = sc.nextInt();
			if( point[a]==0 ){
				D[a] = b;
				point[a] = 1;
			}else{
				if( D[a]!=b ){
					D[a] = -1;
					ans = 1;
				}
			}
		}
		if( point[1]==0 && N>1 ){
			D[1] = 1;          
        }          
		if( point[1]==1 && N>1 && D[1]==0 ){
			ans = 1;
		}
		if( ans==1 ){
			System.out.println(-1);
		}else{
			if( N==1 ){
				System.out.print(D[1]);
			}
			if( N==2 ){
				System.out.print(D[1]);
				System.out.print(D[2]);
			}
			if( N==3 ){
				System.out.print(D[1]);
				System.out.print(D[2]);
				System.out.print(D[3]);
			}
		}
	}
}
