#include using namespace std; using ll = long long; using ld = long double; using pll = pair; constexpr ll MOD = 1e9 + 7; //constexpr ll MOD = 998244353; //constexpr ll MOD = ; ll mod(ll A, ll M) {return (A % M + M) % M;} constexpr ll INF = 1LL << 60; template bool chmin(T& a, T b) {if (a > b) {a = b; return true;} return false;} template bool chmax(T& a, T b) {if (a < b) {a = b; return true;} return false;} ll divceil(ll A, ll B) {return (A + (B - 1)) / B;} #define FINALANS(A) do {cout << (A) << '\n'; exit(0);} while (false) int main() { ll a, b, c; cin >> a >> b >> c; ld s = (a + b + c) / 2.0; ld S = sqrt(s * (s - a) * (s - b) * (s - c)); ld ans = S / 4.0; cout << setprecision(15) << ans << endl; }