#include <bits/stdc++.h>
int main() {
  int a, x, y, k = 0, c = 0, x2;
  float xc;
  scanf("%d %d %d", &a, &x, &y);
  if (a < 1 || a > 100 || x < -1000000 || x > 1000000 || y < 0 || y > 1000000)
    printf("-1");
  else {
    xc = (float)a / 2;
    x2 = a / 2;
    if (x > -a && x < a) {
      if ((x != xc && xc != y) || (x2 % 2 == 1 && x2 != x) ||
          (a % 2 == 0 && x2 % 2 == 1)) {
        if (y % a != 0) {
          if (y < a && x > -xc && x < xc)
            printf("1");
          else {
            while (k <= y) {
              k = k + a;
              c++;
            }
            if (c % 2 == 0) {
              if ((a == 2 && x == -xc) || (a == 2 && x == xc))
                printf("-1");
              else {
                if (xc > x)
                  printf("%d", c + (c / 2 - 1));
                else
                  printf("-1");
              }
            } else {
              if (x != 0) {
                if (x < 0 && y > a)
                  printf("%d", c + (c / 2 - 1));
                else if (y > a)
                  printf("%d", c + (c / 2 - 1) + 1);
                else
                  printf("-1");
              } else
                printf("-1");
            }
          }
        } else
          printf("-1");
      } else
        printf("-1");
    } else
      printf("-1");
  }
  return 0;
}
