#include <bits/stdc++.h>
typedef long long ll;
#define INF 1000000000
#define MOD 1000000007
using namespace std;
int main(void){
    ll l;
    cin>>l;
    ll num_aba=(l-1)/2,num_bab=num_aba-1;

    ll ans=0;
    while(num_aba>0){
        ans+=num_aba+num_bab;
        num_aba--;
        num_bab--;
    }
    cout<<ans<<endl;
}