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.ArrayList;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

	class P{
		int s;
		int c;
		P(int s, int c){
			this.s=s;
			this.c=c;
		}
	}

	public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int m=sc.nextInt();

		ArrayList<P> p = new ArrayList<P>();
		for(int i=0; i<m; i++) {
			p.add(new P(sc.nextInt(),sc.nextInt()));
		}

		for(int i=0; i<1000; i++) {
			ArrayList<Integer> d = new ArrayList<Integer>();
			d.add(i%10);
			int ni = i/10;
			int keta=1;
			while(ni>0) {
				d.add(0,ni%10);
				ni /= 10;
				keta++;
			}
			if(keta != n) continue;

			boolean ok = true;
			for(int j=0 ;j<p.size(); j++) {
				int s = p.get(j).s;
				int c = p.get(j).c;
				if(d.get(s-1) != c) {
					ok = false;
				}
			}
			if(ok) {
				System.out.println(i);
				sc.close();
				return;
			}
		}
		System.out.println(-1);
		sc.close();
	}
}
