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.*;
import java.io.*;
import java.math.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        boolean first0 = false;
        char[] ans = new char[n];
        for(int i = 0; i < n; i++){
            ans[i] = '0';
        }
        for(int i = 0; i < m; i++){
            int s = sc.nextInt();
            char c = sc.next().charAt(0);
            if(s == 1 && c == '0'){
                first0 = true;
            }
            if(ans[s-1] != '0' && ans[s-1] != c){
                System.out.println(-1);
                return;
            }else{
                ans[s-1] = c;
            }
        }
        if(n != 1 && ans[0] == '0' && first0){
            System.out.println(-1);
            return;
        }else if(n != 1 && ans[0] == '0'){
            ans[0] ='1';
        }
        System.out.println(new String(ans));
    }
}
