// yukicoder My Practice
// author: Leonardone @ NEETSDKASU
#include <iostream>
#include <algorithm>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

// const ll MD = 1000000007LL;
// const ull MD = 1000000007ULL;


void solve() {
    /*
    a0 = x
    a1 = a0 + 1 = x + 1
    a2 = a1 + 1 = x + 2
    s[3] = x + (x + 1) + (x + 2)
    s[3] = 3 * x + ns(3 - 1)
    n * a0 + n * (n - 1) / 2
    n * (2 * a0 + n - 1) / 2
    */
    
    ll n;
    cin >> n;
    
    if (n % 2ULL == 0ULL) {
        n >>= 1;
    }
    
    cout << n << endl;
}










int main() { solve(); return 0; }