#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    int n, k;
    cin >> n >> k;

    printf("%.8f\n", n * 0.5);

    return 0;
}