#include <bits/stdc++.h>
using namespace std;

template <class T> int sz(T&& a) { return int(size(forward<T>(a))); }

template <class T> using vc = vector<T>;
template <class T> using vvc = vc<vc<T>>;

using ll = int64_t;
using vi = vc<int>;

template <class F>
struct ycr {
	F f;
	
	template <class T>
	explicit ycr(T&& f_) : f(forward<T>(f_)) {}

	template <class... Args>
	decltype(auto) operator()(Args&&... args) {
		return f(ref(*this), forward<Args>(args)...);
	}
};
template <class F>
decltype(auto) yc(F&& f) {
	return ycr<decay_t<F>>(forward<F>(f));
}

using D = double;

int main() {
	ios_base::sync_with_stdio(false), cin.tie(nullptr);
	cout << fixed << setprecision(42);

	int W, H, N; cin >> W >> H >> N;

	vector<D> logs(N+2);
	for (int a = 1; a <= N+1; a++) {
		logs[a] = log(a);
	}

	vector<D> fact(N+1);
	for (int i = 1; i <= N; i++) {
		fact[i] = fact[i-1] + logs[i];
	}

	const D c = fact[N] + log(H) + log(W) - N * log(2);
	D ans = 0.;
	for (int k = 0; k <= N; k++) {
		ans += exp(c - fact[k] - fact[N-k] - 2 * (logs[k+1] + logs[N-k+1]));
	}
	cout << ans << '\n';
}