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