#include <bits/stdc++.h>
using namespace std;
template <class T>
inline void smn(T &a, const T &b) {
  if (b < a) a = b;
}
template <class T>
inline void smx(T &a, const T &b) {
  if (b > a) a = b;
}
template <class T>
inline T rev(const T &a) {
  T _ = a;
  reverse(_.begin(), _.end());
  return _;
}
const double eps = 1e-9;
const long double leps = 1e-14;
int a, x, y;
int main(int argc, char *argv[]) {
  ios_base::sync_with_stdio(false);
  cin >> a >> x >> y;
  if (y % a == 0) {
    cout << -1 << '\n';
    return 0;
  }
  if (y < a) {
    if (2 * abs(x) >= a)
      cout << -1 << '\n';
    else
      cout << 1 << '\n';
    return 0;
  }
  y -= a;
  int t = y / a;
  int now = 2 + 3 * (t / 2);
  if (t % 2 == 1) now++;
  if (t % 2 == 0) {
    if (2 * abs(x) >= a)
      cout << -1 << '\n';
    else
      cout << now << '\n';
    return 0;
  }
  if (abs(x) >= a || x == 0)
    cout << -1 << '\n';
  else if (x < 0)
    cout << now << '\n';
  else
    cout << now + 1 << '\n';
  return 0;
}
