#include <bits/stdc++.h>
using namespace std;
long long int f1(long int x, long int a) {
  if ((x < 0 && x > (-1 * ((double)a) / 2)) || (x > 0 && x < ((double)a) / 2) ||
      x == 0)
    return 1;
  else
    return 0;
}
long long int f2(long long int x, long long int a) {
  if ((x < 0 && x > (-1 * ((double)a))) || (x > 0 && x < ((double)a)))
    return 1;
  else
    return 0;
}
int main() {
  long long int x, y, a, num, p, flag = 1, ans;
  cin >> a >> x >> y;
  num = (y - a) % (2 * a);
  ans = (y - a - num) / a;
  ans = 1 + (ans / 2) * 3;
  p = num / a;
  if (p * a == num)
    flag = 0;
  else {
    if (y < a) {
      if (!f1(x, a)) flag = 0;
    } else {
      if (p < 1) {
        if (f1(x, a))
          ans += 1;
        else
          flag = 0;
      } else {
        if (f2(x, a)) {
          if (x < 0)
            ans += 2;
          else
            ans += 3;
        } else
          flag = 0;
      }
    }
  }
  if (flag)
    cout << ans;
  else
    cout << -1;
  return 0;
}
