#include <stdio.h>
#include "trilib.h"
#include <string.h>
#include <stdlib.h>
int sta[55555], top, n, low[55555], q, w, a[55555], b[55555], c, d, ch_high[55555], ch_low[55555], cha, chb
, sta2[55555], top2;
int cmp_high(const void *ii, const void *jj) {
return ! is_clockwise(q, *(int*)ii, *(int*)jj);
}
int cmp_low(const void *ii, const void *jj) {
return ! is_clockwise(q, *(int*)ii, *(int*)jj);
}
int main() {
n = get_n();
q = 1;
w = 2;
for (int i = 3; i <= n; ++i) {
if (is_clockwise(q, w, i)) {
low[i] = 1;
a[c++] = i;
} else {
low[i] = 0;
b[d++] = i;
}
}
qsort(b, d, sizeof *b, cmp_high);
qsort(a, c, sizeof *a, cmp_low);
sta[top = 1] = w;
for (int i = 0; i < d; ++i) {
int j = b[i];
while (top >= 2 && is_clockwise(sta[top - 1], sta[top], j))
--top;
sta[++top] = j;
}
while (top >= 2 && is_clockwise(sta[top - 1], sta[top], q))
--top;
sta[++top] = q;
cha = top;
memcpy(ch_high, sta, sizeof sta);
sta[top = 1] = q;
for (int i = 0; i < c; ++i) {
int j = a[i];
while (top >= 2 && is_clockwise(sta[top - 1], sta[top], j))
--top;
sta[++top] = j;
}
while (top >= 2 && is_clockwise(sta[top - 1], sta[top], w))
--top;
sta[++top] = w;
chb = top;
memcpy(ch_low, sta, sizeof sta);
if (cha == 0) {
give_answer(chb);
return 0;
}
if (chb == 0) {
give_answer(cha);
return 0;
}
for (int i = 2; i < cha; ++i)
sta[++top] = ch_high[i];
for (int i = 1; i <= top; ++i) {
int j = sta[i];
while (top2 >= 2 && is_clockwise(sta2[top2 - 1], sta2[top2], j))
--top2;
sta2[++top2] = j;
}
give_answer(top2);
return 0;
}
