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
#include<bits/stdc++.h>

using namespace std;

int main() {
  int n, m, s, c;
  cin >> n >> m;
  vector<int> num(n, -1);
  while (m--) {
    cin >> s >> c;
    if (num[--s] != -1 && num[s] != c || n > 1 && !s && !c) {
      cout << -1 << '\n';
      return 0;
    }
    num[s] = c;
  }
  for (int i = 0; i < n; ++i)
    cout << (num[i] == -1 ? (n > 1 && !i) : num[i]);
  cout << '\n';
  return 0;
}