#include <bits/stdc++.h>
using namespace std;
int a, x, y;
int main() {
  cin >> a >> x >> y;
  if (x > -a && x < a) {
    if (2 * x > -a && 2 * x < a) {
      if (y > 0 && y < a) {
        cout << 1 << endl;
        return 0;
      }
      if (y > a && y < 2 * a) {
        cout << 2 << endl;
        return 0;
      }
    }
    if (y <= 2 * a) {
      cout << -1 << endl;
      return 0;
    }
    int d = y;
    d -= 2 * a;
    if (d % a == 0) {
      cout << -1 << endl;
      return 0;
    }
    d /= a;
    if (d % 2 == 1) {
      if (2 * x > -a && 2 * x < a) {
        cout << 5 + (d / 2) * 3 << endl;
        return 0;
      }
      cout << -1 << endl;
      return 0;
    } else {
      if (x > -a && x < a && x != 0) {
        int r = 3 + (d / 2) * 3;
        if (x > 0) r++;
        cout << r << endl;
        return 0;
      }
      cout << -1 << endl;
      return 0;
    }
    cout << -1 << endl;
    return 0;
  }
  cout << -1 << endl;
  return 0;
}
