#include <bits/stdc++.h>
using namespace std;
int main() {
  long long a, x, y, i;
  cin >> a >> x >> y;
  if (y % a == 0)
    cout << "-1\n";
  else {
    if (y < 2 * a) {
      y = y / a;
      if (a % 2 == 0 && (x >= a / 2 || x <= -a / 2))
        cout << "-1\n";
      else if (a % 2 != 0 &&
               ((x >= ceil((float)a / 2) || (x <= -ceil((float)a / 2)))))
        cout << "-1\n";
      else
        cout << y + 1 << "\n";
    } else {
      y = y - 2 * a;
      long long c = floor(y / a);
      if (c % 2 == 0) {
        long long b = (y / (2 * a));
        long long ans = 2 + 2 * b + b;
        if (x >= a || x <= -a || x == 0)
          cout << "-1\n";
        else if (x > 0 && x < a)
          cout << ans + 2;
        else
          cout << ans + 1;
      } else {
        long long b = (y / (2 * a));
        long long ans = 2 + 2 * (b + 1) + b;
        if (a % 2 == 0 && (x >= a / 2 || x <= -a / 2))
          cout << "-1\n";
        else if (x >= ceil((float)a / 2) || x <= -ceil((float)a / 2))
          cout << "-1\n";
        else
          cout << ans + 1 << "\n";
      }
    }
  }
  return 0;
}
