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 {
	private static int[] ans;
  	private static int n;
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
    	n = sc.nextInt();
    	int m = sc.nextInt();

    	ans = new int[n];
    	for (int i = 0; i < n; i++) {
    		ans[i]=-1;
    	}
    	for (int i = 0; i < m; i++) {
	    	int s = sc.nextInt();
	    	int c = sc.nextInt();

    		if (!aaa(s,c)) {
    			System.out.println(-1);
    			return;
    		} 
    	}
    	if (check()) {

    	} else {
			System.out.println(-1);
			return;
    	}
    }
    private static boolean check() {
    	if (ans[0]==0 && n!=1) {
    		return false;
    	}
    	for (int i=0;i< ans.length; i++) {
    		if (ans[i]==-1){
    			if(i==0 && n!=1){
    		System.out.print(1);
}else{
    		System.out.print(0);
}
    		}else{
    		System.out.print(ans[i]);
    	}
    	}
		return true;
    }
    private static boolean aaa(int s, int c) {
    	if (s > n) {
    		return false;
    	}
    	if (ans[s-1]!=-1 && ans[s-1]!=c ) {
    		return false;
    	}
    	ans[s-1]=c;
    	return true;
    }
}



