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{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int M = sc.nextInt();
    int flg = 0;
    if(N == 1 && M == 0){
        System.out.println("0");
        flg = 1;
    }
    int[] n = new int[N];
    int[] flg2 = new int[N];
    for(int i = 0; i < M; i++){
      int s = sc.nextInt();
      int c = sc.nextInt();
      if(N == 1 && M == 1){
        System.out.println(c);
        flg = 1;
        break;
      } else if(s == 1 && c == 0){
        System.out.println("-1");
        flg = 1;
        break;
      } else if(n[s - 1] == 0 || n[s - 1] == c || flg2[s - 1] == 0){
        n[s - 1] = c;
        flg2[s - 1] = 1;
      } else {
        System.out.println("-1");
        flg = 1;
        break;
      }
    }
    if(N != 1 && n[0] == 0){
      n[0] = 1;
    }
    if(flg == 0){
      for(int i = 0; i < N; i++){
        System.out.print(n[i]);
      }
    }
  }
}
