#include "bits/stdc++.h"
#pragma warning(disable:4996)
using namespace std;
#define int long long
#define rep(i,n) for(int i=0;i<n;i++)
typedef pair<int, int> P;
const long long mod = 1000000007;
const long long inf = 1ll<<61;

signed main() {
	double n; cin >> n;
	double ans = n / 2;
	printf("%.13lf\n", ans);
}