#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using vi = vector<int>;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int a, x, y;
  cin >> a >> x >> y;
  x <<= 1;
  y <<= 1;
  if (y % (2 * a) == 0) {
    cout << -1 << '\n';
    return 0;
  }
  if (y < 2 * a) {
    if (-a < x and x < a) {
      cout << 1 << '\n';
      return 0;
    } else {
      cout << -1 << '\n';
      return 0;
    }
  }
  y -= 2 * a;
  int base = y / 4 / a;
  y %= 4 * a;
  if (y < 2 * a) {
    if (-a < x and x < a) {
      cout << (2 + 3 * base) << '\n';
      return 0;
    }
  } else {
    if (-2 * a < x and x < 0) {
      cout << (3 + 3 * base) << '\n';
      return 0;
    } else if (0 < x and x < 2 * a) {
      cout << (4 + 3 * base) << '\n';
      return 0;
    }
  }
  cout << -1 << '\n';
  return 0;
}
