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.Scanner;

public class Main {
    public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
    	try {
    		final int n = sc.nextInt();
    		final int m = sc.nextInt();

    		int [] s = new int[m];
    		char [] c = new char[m];
    		for (int i=0; i<m; i++) {
    			s[i] = sc.nextInt();
    			c[i] = sc.next().charAt(0);
    		}

    		if (n == 1 && m == 0) {
    			System.out.println(0);
    			return;
    		}

    		char [] str = new char[n];
    		boolean [] modified = new boolean[n];
    		str[0] = '1';
			modified[0] = false;
    		for (int i=1; i<n; i++) {
    			str[i] = '0';
    			modified[i] = false;
    		}

    		for (int i=0; i<m; i++) {
    			if (modified[s[i]-1] && str[s[i]-1] != c[i]) {
        			System.out.println("-1");
        			return;
    			} else {
        			str[s[i]-1] = c[i];
        			modified[s[i]-1] = true;
    			}
    		}

    		if (n > 1 && str[0] == '0') {
    			System.out.println("-1");
    		} else {
        		for (int i=0; i<n; i++) {
        			System.out.print(str[i]);
        		}
        		System.out.println();
    		}

    	} finally {
    		sc.close();
    	}
    }
}
