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.*;

class Main {

	static Scanner sc = new Scanner(System.in);

	public static void main(String[] args) {
		int N=sc.nextInt(),M=sc.nextInt(),s[]=new int[M],c[]=new int[M];
		Map<Integer,Integer> a=new HashMap<Integer,Integer>();
		int ans=0;
		for(int i=0;i<M;i++) {
			s[i]=sc.nextInt();
			c[i]=sc.nextInt();
			if(!a.containsKey(s[i]-1)) {
				a.put(s[i]-1, c[i]);
			}else {
				if(a.get(s[i]-1)!=c[i]) {
					ans=-1;
					break;
				}
			}
		}
		if(a.containsKey(0)&&N!=1)if(a.get(0)==0)ans=-1;
		if(M==0&&N==1) ans=0;
		else if(ans!=-1) {
			for(int i=0;i<N;i++) {
				if(a.containsKey(i)) {
					ans+=a.get(i)*(int)Math.pow(10,N-i-1);
				}else if(i==0){
					ans+=(int)Math.pow(10, N-1);
				}
			}
		}
		System.out.println(ans);
	}
}