#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <optional>
#include <queue>
#include <set>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std; // NOLINT

int main() {
    int64_t n;
    cin >> n;
    int64_t ans = 0;
    for (auto i = 0; i <= n; ++i) {
        ans = max(ans, (i + 1) * (n - i + 1) - 1);
    }
    cout << ans << endl;
    return 0;
}