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.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int N = sc.nextInt();
		int M = sc.nextInt();
		int[] v = new int[N];
		Arrays.fill(v, -1);
		
		for(int i=0; i<M; i++) {
			int s = sc.nextInt()-1;
			int c = sc.nextInt();
			
			if(v[s]<0) {
				v[s] = c;
			} else if(v[s]!=c) {
				System.out.println(-1);
				sc.close();
				return;
			}
		}
		if(N>1 && v[0]==0) {
			System.out.println(-1);
			sc.close();
			return;
		}
		for(int i=0; i<N; i++) {
			System.out.print(v[i]>=0 ? v[i] : (i==0 ? (N==1 ? 0 : 1) : 0));
		}
		System.out.println();
		sc.close();
	}
}
