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;
  cin >> n >> m;
  vector<pair<int, char>> p(m);

  for (int i = 0; i < m; i++) cin >> p.at(i).first >> p.at(i).second;

  for (int i = 0; i <= 1000; i++) {
    string s = to_string(i);
    if (s.size() != n) continue;
    bool ok = true;
    for (int j = 0; j < m; j++) {
      if (s.at(p.at(j).first - 1) != (p.at(j).second)) ok = false;
    }
    if (ok) {
      cout << i << endl;
      return 0;
    }
  }
  cout << -1 << endl;

  return 0;
}
