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;
  map<int, int> mp;
  bool ok=1;
  for (int i = 0; i < m; i++) {
    int pos, tmp; cin >> pos >> tmp;
    if (mp.find(pos) != mp.end() && mp[pos] != tmp) ok=0;
    if (pos == 1 && tmp == 0 && n != 1)
      ok = 0;
    mp[pos] = tmp;
  }
  if (!ok) cout << -1;
  else {
    for (int i = 1; i <= n; i++)
      cout << (mp.find(i) != mp.end() ? mp[i] : i == 1 && n != 1 ? 1 : 0);
  }
  return 0;
}
