#include<bits/stdc++.h>

using namespace std;

#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define pf push_front
#define LC k<<1
#define RC k<<1|1
#define IO cin.sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define all(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define rep(i, a, n) for (int i = a; i < n; i++)
#define repn(i, a, n) for (int i = a; i <= n; i++)
#define per(i, a, n) for (int i = (n) - 1; i >= a; i--)
#define pern(i, a, n) for (int i = n; i >= a; i--)

typedef long long LL;
typedef long double LD;
typedef unsigned long long ull;
typedef pair<int, int> PII;
typedef pair<int, LL> PIL;
typedef pair<LL, int> PLI;
typedef pair<double, double> PDD;
typedef pair<ull, ull> PUU;
typedef pair<LL, LL> PLL;

const int N = 1100000;
const int M = 1100000;
const int mod = 1e9+7;
const int inf = (int)1e9;
const LL INF = 1e18;
const double eps = 1e-9;

mt19937_64 Rand((unsigned long long)new char);
#define rand Rand

const int L = 400;

int n, cnt[N];
LD w, h;
int main() {
	IO;
	cin >> w >> h >> n;
	LD ans = 0;
	int st = max(n / 2 - L, 0), ed = min(n / 2 + L, n);
	repn(i, st, ed) {
		memset(cnt, 0, sizeof(cnt));
		repn(j, 0, i) {
			cnt[j] = n / (i + 1);
			if (n % (i + 1) > j) cnt[j]++;
		}
		LD p = w * h;
		repn(j, 1, cnt[0]) p = p / 2.0;
		repn(j, 1, i) {
			p = p * (n - j + 1) / j;
			repn(k, 1, cnt[j]) p = p / 2.0;
		}
		p /= (i + 1);
		p /= (i + 1);
		p /= (n - i + 1);
		p /= (n - i + 1);
		ans += p;
	}
	cout << fixed << setprecision(15) << (double)ans << "\n";
	return 0;
}