#include <bits/stdc++.h>
using namespace std;
class square {
 public:
  int lx, ly, rx, ry;
  void move(int dx, int dy) {
    lx += dx;
    rx += dx;
    ly += dy;
    ry += dy;
  }
  void init(int a) {
    lx = -a / 2;
    ly = 0;
    rx = lx + a;
    ry = ry + a;
  }
};
square s[3];
int main() {
  int a, x, y;
  scanf("%i%i%i", &a, &x, &y);
  a *= 2;
  x *= 2;
  y *= 2;
  if ((-a / 2 < x) && (x < a / 2) && (0 < y) && (y < a)) {
    printf("1");
    return 0;
  }
  y -= a;
  for (int i = 0; i < 3; i++) s[i].init(a);
  int solve = 1;
  s[1].move(-a / 2, a);
  s[2].move(+a / 2, a);
  solve += 3 * (y / (2 * a));
  y = y % (2 * a);
  for (int i = 0; i < 3; i++)
    if ((s[i].lx < x) && (x < s[i].rx) && (s[i].ly < y) && (y < s[i].ry)) {
      printf("%i", solve + i + 1);
      return 0;
    }
  printf("-1");
}
