#include <bits/stdc++.h>
#define all(a) begin(a), end(a)
#define int long long
using namespace std;

typedef long double LD;
const int N = 2e3 + 11;
LD dp[N][N];
void solve() {
	int n, m, p; cin >> n >> m >> p;
	--n; --m;
	for (int i = 0; i <= n; i++) for (int j = 0; j <= m; j++)
		dp[i][j] = 1LL << 60;
	dp[0][0] = 0;
	for (int i = 0; i <= n; i++) {
		for (int j = 0; j <= m; j++) {
			if (i == 0 || j == 0) dp[i][j] = (i + j) * (LD) p / 4;
			else {
				LD a = dp[i - 1][j], b = dp[i][j - 1];
				if (a > b) swap(a, b);
				LD mid = min(a + p, b);
				LD E = a / 2 + ((a + mid) * (mid - a) / 2 + (p - (mid - a)) * b) / p / 2;
				dp[i][j] = E;
			}
		}
	}
	// for (int i = 0; i <= n; i++) {
	// 	for (int j = 0; j <= m; j++) {
	// 		cout << dp[i][j] << ' ';
	// 	}
	// 	cout << '\n';
	// }
	cout << fixed << setprecision(10) << dp[n][m] << '\n';
}

int32_t main(){
#ifndef LOCAL
	cin.tie(0)->sync_with_stdio(false);
#endif
	int t = 1;
	// cin >> t;
	while (t--) {
		solve();
	}
}