#include <iostream>
#include <fstream>
#include <algorithm>
#include <iomanip>
#include <random>
#include <ctime>
#include <bitset>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <cmath>
#include <climits>
#include <cstring>
#include <queue>
#include <deque>
#include <list>
#include <stack>

#define pb push_back
#define ff first
#define ss second
#define sqr(x) (x) * (x)
#define cb(x) (x) * (x) * (x)
#define SIZE 101
#define INF 1e18 + 9


using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int inf = 2e9;
const ll linf = 2e18;
const ll mod = 1e9 + 7;

template <typename T>
ostream& operator << (ostream& s, vector<T>& v) {
    for (auto el : v) {
        s << el << " ";
    }
    return s;
}

typedef vector<int> graf_line;
typedef vector<graf_line> graf;

typedef vector<int> vint;
typedef vector<vint> vvint;


int main() {

    int n;
    cin >> n;
    vvint c(n, vint(n));
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++){
            if (j > i) c[i][j] = j - i;

        }
    vvint f(n, vint(n));
    for (;;)
    {

        vint from(n, -1);
        vint q(n);
        int h = 0, t = 0;
        q[t++] = 0;
        from[0] = 0;
        for (int cur; h < t;)
        {
            cur = q[h++];
            for (int v = 0; v < n; v++)
                if (from[v] == -1 &&
                    c[cur][v] - f[cur][v] > 0)
                {
                    q[t++] = v;
                    from[v] = cur;
                }
        }

        if (from[n - 1] == -1)
            break;
        int cf = inf;
        for (int cur = n - 1; cur != 0; )
        {
            int prev = from[cur];
            cf = min(cf, c[prev][cur] - f[prev][cur]);
            cur = prev;
        }

        for (int cur = n - 1; cur != 0; )
        {
            int prev = from[cur];
            f[prev][cur] += cf;
            f[cur][prev] -= cf;
            cur = prev;
        }

    }

    int flow = 0;
    for (int i = 0; i < n; i++)
        if (c[0][i])
            flow += f[0][i];

    cout << flow;

}