#include <bits/stdc++.h>
using namespace std;
const long long INF = 1LL << 60;
long long a, x, y, s, k;
int main() {
  cin >> a >> x >> y, s++, k = y / a;
  k % 2 == 0 ? (x == 0 ? s = -1 : (x > 0 ?: s--))
             : ((float)a / 2 - abs(x) > 0 ?: s = -1);
  s >= 0 ? s += k / 2 * 3 + ((k + 1) % 2 == 0 ? 1 : 0) : s = -1;
  k != 0 ?: ((float)a / 2 - abs(x) > 0 ? s = 1 : s = -1);
  if (abs(x) >= a || y % a == 0) s = -1;
  cout << (s > 0 ? s : -1) << endl;
}
