#include <bits/stdc++.h>

using namespace std;

using int128 = __int128_t;

#define rep(i, n)         for (int i = 0; i < n; ++i)
#define reps(i, n, s)     for (int i = 0; i < n; i += s)
#define repl(i, l, r)     for (int i = l; i < r; ++i)
#define repsl(i, l, r, s) for (int i = l; i < r; i += s)

#define all(iterable) (iterable).begin(), (iterable).end()

constexpr int dx4[4] = {1, 0, -1, 0};
constexpr int dy4[4] = {0, 1, 0, -1};

constexpr int dx8[8] = {1, 1, 0, -1, -1, -1, 0, 1};
constexpr int dy8[8] = {0, 1, 1, 1, 0, -1, -1, -1};

template <typename T>
void print(const vector<T>& vec, const string sep = " ", const string end = "\n") {
    int n = vec.size();
    rep(i, n) {
        cout << vec[i];
        if (i < n - 1) cout << sep;
        else cout << end;
    }
}

template <typename T>
void read(vector<T>& a, int begin_index, int length) {
    if (a.size() < begin_index + length) a.resize(begin_index + length);
    while (length --> 0) cin >> a[begin_index++];
}
template <typename T>
void read(vector<T>& a) { read(a, 0, a.size()); }

int main() {
    int a, b, c;
    cin >> a >> b >> c;
    long double s = (long double) (a + b + c) / 2.;
    long double S = sqrtl(s * (s - a) * (s - b) * (s - c));
    cout << fixed << setprecision(20) << S / 4. << '\n';
    return 0;
}