#include <bits/stdc++.h>
using namespace std;
long long max(long long a, long long b) {
  if (a > b) return a;
  return b;
}
long long min(long long a, long long b) {
  if (a < b) return a;
  return b;
}
int main() {
  int a, x, y;
  cin >> a >> x >> y;
  if (y % a == 0) {
    cout << -1 << endl;
    return 0;
  }
  y /= a;
  if (y == 0) {
    if (x < double(a) / 2.0 && x > -(double(a) / 2.0))
      cout << 1 << endl;
    else
      cout << -1 << endl;
    return 0;
  }
  if (y % 2) {
    if (x < double(a) / 2.0 && x > -(double(a) / 2.0)) {
      int now = 2;
      for (int i = 1; i < y; i++) {
        if (i % 2) now++;
        now++;
      }
      cout << now << endl;
      cin >> now;
    } else
      cout << -1 << endl;
  } else {
    if (x < a && x > -(a) && x != 0) {
      int now = 2;
      for (int i = 1; i < y; i++) {
        if (i % 2) now++;
        now++;
      }
      if (x > 0) now++;
      cout << now - 1 << endl;
      cin >> now;
    } else
      cout << -1 << endl;
  }
}
