#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
template<class t> using vc = vector<t>;
template<class t> using vvc = vc<vc<t>>;
using pi = pair<int,int>;
using pl = pair<ll,ll>;
using vi = vc<int>;
using vvi = vvc<int>;
using vl = vc<ll>;
using vvl = vvc<ll>;

#define rep(i,a,b) for (int i = (a); i < (b); i++)
#define irep(i,a,b) for (int i = (a); i > (b); i--)
#define all(a) a.begin(),a.end()
#define print(n) cout << n << '\n'
#define pritn(n) print(n)
#define printv(n,a) {copy(all(n),ostream_iterator<a>(cout," ")); cout<<"\n";}
#define printvv(n,a) {for(auto itr:n) printv(itr,a);}
#define rup(a,b) (a+b-1)/b
#define input(A,N) rep(i,0,N) cin>>A[i]
#define chmax(a,b) a = max(a,b)
#define chmin(a,b) a = min(a,b)


int main(){
    cout << fixed << setprecision(15);
    
    ll l;
    cin>>l;
    ll a,b;
    a = (l+1)/2;
    b = l/2;
    print(a*(a-1)/2+b*(b-1)/2);
    
    //system("pause");
    return 0;
}