// MagicDark
#include <bits/stdc++.h>
#define debug cerr << "\033[32m[" << __LINE__ << "]\033[0m "
#define SZ(x) ((int) x.size() - 1)
#define all(x) x.begin(), x.end()
#define ms(x, y) memset(x, y, sizeof x)
#define F(i, x, y) for (int i = (x); i <= (y); i++)
#define DF(i, x, y) for (int i = (x); i >= (y); i--)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
template <typename T> T& chkmax(T& x, T y) {return x = max(x, y);}
template <typename T> T& chkmin(T& x, T y) {return x = min(x, y);}
template <typename T> T& read(T &x) {
	x = 0; int f = 1; char c = getchar();
	for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;
	for (; isdigit(c); c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);
	return x *= f;
}
const int N = 1010;
const double eps = 1e-6;
int n, m, p;
double f[N][N];
signed main() {
	read(n), read(m), read(p);
	n--, m--;
	F(i, 0, n)
		F(j, 0, m) {
			if (!i && !j) continue;
			if (!i) {
				f[i][j] = f[i][j - 1] + (p) / 4.0;
				// debug << "~ " << f[i][j] << endl;
				// debug << "~ " << f[i][j] << endl;
				// continue;
			} else if (!j) {
				f[i][j] = f[i - 1][j] + (p) / 4.0;
				// continue;
			} else {
				// if (i == n && j == m) {
				// 	double a = f[i - 1][j], b = f[i][j - 1];
				// 	if (a > b) swap(a, b);
				// 	f[i][j] += 0.5 * a;
				// 	double delta = b - a;
				// 	int t = delta + eps;
				// 	chkmin(t, p);
				// 	// debug << "! " << a << " " << b << " " << t << endl;
				// 	// debug << "~ " << i << " " << j << ' ' << t << endl;
				// 	f[i][j] += (double) (t + 1) / ((p + 1) * 2) * (a + t / 2.0) + (double) (p - t) / ((p + 1) * 2) * b;
				// 	continue;
				// }
				double a = f[i - 1][j], b = f[i][j - 1];
				if (a > b) swap(a, b);
				f[i][j] += 0.5 * a;
				double t = b - a;
				// t t = delta + eps;
				chkmin(t, (double) p);
				// debug << "! " << a << " " << b << " " << t << endl;
				// debug << "~ " << i << " " << j << ' ' << t << endl;
				f[i][j] += (double) (t) / (p * 2) * (a + (t) / 2.0) + (double) (p - t) / (p * 2) * b;
				// f[i][j] = max(f[i][j])
			}
			// debug << i << " " << j << " " << f[i][j] << endl;
		}
	cout << fixed << setprecision(10) << f[n][m];
	return 0;
}
/* why?
*/