#include<iostream> #include<list> using namespace std; typedef long long ll; int main(){ int n; cin >> n; if(n==1){ cout << 0 << endl; return 0; } ll ans = 0; list<ll> l; int low = 1, high = n; l.push_back(high--); while(low <= high){ if(low <= high) l.push_front(low++); if(low <= high) l.push_back(low++); if(low <= high) l.push_front(high--); if(low <= high) l.push_back(high--); } auto it = l.begin(); while(it != l.end()){ auto nit = it; nit++; if(nit == l.end()) nit = l.begin(); ans += (*it) * (*nit); it++; } cout << ans << endl; return 0; }