#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long a, x, y;
  cin >> a >> x >> y;
  if (y % a == 0)
    cout << -1;
  else {
    long long ratio = (long long)(y / a);
    if (ratio > 0) {
      if (((long long)(y / a)) % 2 == 1) {
        if (2 * abs(x) < a)
          cout << 2 * ratio - (long long)(ratio / 2);
        else
          cout << -1;
      } else {
        if (x != 0 && abs(x) < a && x < 0)
          cout << 2 * ratio - (ratio / 2);
        else if (x != 0 && abs(x) < a && x > 0)
          cout << 2 * ratio - (ratio / 2) + 1;
        else
          cout << -1;
      }
    } else if (2 * abs(x) < a)
      cout << 1;
    else
      cout << -1;
  }
}
