#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
long long v[40010] , x[40010] , y[40010] , s[40010];
int cmp (int x , int y){
return !is_clockwise(1 , x , y);
}
int main()
{
long long n , i , elem , j , aux , sol;
n = get_n();
/// stergi citirea, folosesti get_n
for (i = 1 ; i <= n ; i++)
v[i] = i;
sort (v + 2 , v + n + 1 , cmp);
/*for (i = 1 ; i <= n ; i++){
fprintf (fout,"%d\n" , v[i]);
}*/
sol = 3;
for (i = 1 ; i <= n ; i++){
s[1] = v[1];
s[2] = v[2];
elem = 2;
for (j = 3 ; j <= n ; j++){
while (elem >= 2 && is_clockwise (s[elem - 1] , s[elem] , v[j]))
elem--;
s[++elem] = v[j];
}
while (elem >= 2 && is_clockwise (s[elem - 1] , s[elem] , s[1]))
elem--;
while (elem >= 2 && is_clockwise (s[elem] , s[1] , s[2]))
elem--;
sol = max(sol , elem);
aux = v[1];
for (j = 2 ; j <= n ; j++)
v[j - 1] = v[j];
v[n] = aux;
}
give_answer((int)sol);
return 0;
}
