#include <bits/stdc++.h>
using namespace std;
bool in(int x, int a, int b) { return x < b && x > a; }
int main() {
  int a, x, y;
  cin >> a >> x >> y;
  a *= 2;
  x *= 2;
  y *= 2;
  if (in(y, 0, a)) {
    cout << (in(x, -a / 2, a / 2) ? 1 : -1) << "\n";
    return 0;
  } else
    y -= a;
  int b = y / (2 * a) * 3;
  y %= 2 * a;
  if (in(y, 0, a) && in(x, -a / 2, a / 2))
    cout << 2 + b;
  else if (in(y, a, 2 * a) && in(x, -a, 0))
    cout << 3 + b;
  else if (in(y, a, 2 * a) && in(x, 0, a))
    cout << 4 + b;
  else
    cout << -1 << "\n";
  return 0;
}
