#include <bits/stdc++.h>
using namespace std;
int main() {
  long a, x, y;
  cin >> a >> x >> y;
  if (y % a == 0)
    cout << "-1";
  else {
    long t = y / a;
    t++;
    if (t == 1 || t % 2 == 0) {
      if (2 * x < a && 2 * x > -a) {
        if (t == 1 || t == 2)
          cout << t;
        else
          cout << (t / 2) * 3 - 1;
      } else
        cout << "-1";
    } else {
      if (x < a && x > -a) {
        if (x > 0) cout << 3 * (t - 1) / 2 + 1;
        if (x < 0) cout << 3 * (t - 1) / 2;
        if (x == 0) cout << "-1";
      } else
        cout << "-1";
    }
  }
}
