#include <bits/stdc++.h>
using namespace std;
int main(int argc, char *argv[]) {
  long long a, x, y;
  cin >> a >> x >> y;
  if (y <= 0) {
    cout << "-1";
    return 0;
  }
  long long b = y % a;
  if (b == 0) {
    cout << "-1";
    return 0;
  }
  long long row, col;
  row = (y - b) / a;
  if (row == 0 || (row % 2) == 1) {
    if (-a < x * 2 && x * 2 < a) {
      if (row == 0)
        cout << 1;
      else
        cout << (row - 1) / 2 * 3 + 2;
    } else
      cout << "-1";
  } else {
    if (-a < x && x < 0)
      cout << row / 2 * 3;
    else if (0 < x && x < a)
      cout << row / 2 * 3 + 1;
    else
      cout << -1;
  }
  return 0;
}
