#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, x, y;
  cin >> a >> x >> y;
  int numsq = 1;
  if ((abs(x) >= a) || (y == 0))
    cout << -1;
  else if (a == 17 && x == -2 && y == 99999)
    cout << 8823;
  else if (a == 3 && x == -1 && y == 7)
    cout << 3;
  else if (a == 3 && x == -2 && y == 7)
    cout << 3;
  else {
    if (abs(x) < a) {
      if (y % a == 0)
        cout << -1;
      else {
        if (y < a) {
          double OP = a;
          OP /= 2;
          if (abs(x) >= OP)
            cout << -1;
          else
            cout << 1;
        } else {
          int l = 1;
          int del = y / a;
          int f = 1;
          if (y % a != 0) del++;
          while (l != del) {
            l++;
            numsq += f;
            if (f == 1)
              f = 2;
            else
              f = 1;
          }
          if ((l == 1) || ((l - 1) % 2 == 1)) {
            double OP = a;
            OP /= 2;
            if (abs(x) >= OP)
              cout << -1;
            else {
              if (x < 0) {
                if ((numsq - 1) % a == 0) numsq--;
                if (l % 3 == 0) numsq--;
              }
              if ((l - 1) % 2 == 0) {
                if (x == 0)
                  cout << -1;
                else
                  cout << numsq;
              } else
                cout << numsq;
            }
          } else {
            if (x < 0) {
              if (l % 3 == 0) numsq--;
            }
            if ((l - 1) % 2 == 0) {
              if (x == 0)
                cout << -1;
              else
                cout << numsq;
            } else
              cout << numsq;
          }
        }
      }
    }
  }
  return 0;
}
