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.Arrays;
import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sn = new Scanner(System.in);
    int N = sn.nextInt();
    int M = sn.nextInt();
    int[] sc = new int[N];
    Arrays.fill(sc, -1);

    // Check inconsistency.
    for (int i = 0; i < M; i++) {
      int s = sn.nextInt();
      int c = sn.nextInt();
      if (sc[s - 1] == -1) {
        sc[s - 1] = c;
      } else if (sc[s - 1] != c) {
        System.out.println(-1);
        return;
      }
    }
    // starting with 0.
    if (sc[0] == 0 && N == 3 || sc[0] == 0 && N == 2) {
      System.out.println(-1);
      return;
    }
    if (sc[0] == -1 && N == 1) {
      System.out.println(0);
      return;
    }
    int ans = sc[0] == -1 ? 1 : sc[0];
    for (int i = 1; i < N; i++) {
      ans *= 10;
      int d = sc[i];
      if (d == -1) {
        d = 0;
      }
      ans += d;
    }
    System.out.println(ans);
  }
}
