#include <bits/stdc++.h>
using namespace std;
#define REP(i, n) FOR(i, 0, (n))
#define FOR(i, a, b) for(int i=(a); i<(b); i++)
#define LAR(a, b) ((a)=max((a),(b)))
#define SML(a, b) ((a)=min((a),(b)))
using ll = long long;
using ld = long double;
using vi = vector<int>;
using vl = vector<ll>;
using pii = pair<int, int>;
using vpii = vector<pair<int, int>>;
template<typename T>
using pque = priority_queue<T, vector<T>, greater<T>>;
#define PB push_back
#define EB emplace_back
#define MP make_pair
#define ALL(a) (a).begin(), (a).end()
#ifdef LOCAL_DEBUG
#define DEBUG(...) printf(__VA_ARGS__)
#else
#define DEBUG(...)
#endif

int main(){
	ld n; scanf("%Lf", &n);
	printf("%Lf\n", n/2);
}