#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
#define pb push_back
#define all(a) a.begin(), a.end()
#define sz(a) ((int)a.size())
const int mod = 1e9 + 7, N = 100000;

#define double long double

int main() {
	ios::sync_with_stdio(false), cin.tie(0);
	int n, m, p;
	cin >> n >> m >> p;
	vector dp(n + 1, vector <double>(m + 1, 1e18));
	for (int i = 1; i <= n; ++i) for (int j = 1; j <= m; ++j) {
		if (i == 1 && j == 1) {
			dp[i][j] = 0;
		} else {
			double a = dp[i - 1][j], b = dp[i][j - 1];
			if (a > b) {
				swap(a, b);
			}
			double cur = a;
			if (b - a <= p) {
				cur += (b * b - a * a) / 2 / p + (1.0 - (b - a) / p) * b;
			} else {
				cur += ((a + p) * (a + p) - a * a) / 2 / p;
			}
			dp[i][j] = cur / 2;
		}
	}
	cout << fixed << setprecision(10) << dp[n][m] << '\n';
}