#include <bits/stdc++.h>
#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...) void(0)
#endif

template <class T> std::istream& operator>>(std::istream& is, std::vector<T>& v) {
    for (auto& e : v) {
        is >> e;
    }
    return is;
}

template <class T> std::ostream& operator<<(std::ostream& os, const std::vector<T>& v) {
    for (std::string_view sep = ""; const auto& e : v) {
        os << std::exchange(sep, " ") << e;
    }
    return os;
}

template <class T, class U = T> bool chmin(T& x, U&& y) {
    return y < x and (x = std::forward<U>(y), true);
}

template <class T, class U = T> bool chmax(T& x, U&& y) {
    return x < y and (x = std::forward<U>(y), true);
}

template <class T> void mkuni(std::vector<T>& v) {
    std::ranges::sort(v);
    auto result = std::ranges::unique(v);
    v.erase(result.begin(), result.end());
}

template <class T> int lwb(const std::vector<T>& v, const T& x) {
    return std::distance(v.begin(), std::ranges::lower_bound(v, x));
}

using ll = long long;

using namespace std;

const double INF = 1e18;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);
    int r, c, p;
    cin >> r >> c >> p;

    double wait = 1.0 * p / 2;
    vector dp(r + 1, vector<double>(c + 1, INF));  // (i, j) にたどり着いてからゴールに到達するまでの待ち時間の期待値
    array<double, 2> tmp;
    for (int i = r - 1; i >= 0; i--) {
        for (int j = c - 1; j >= 0; j--) {
            double& val = dp[i][j];
            if (i == r - 1 and j == c - 1) {
                val = 0;
                continue;
            }
            val = 0;
            tmp[0] = dp[i + 1][j], tmp[1] = dp[i][j + 1];
            for (int _ = 0; _ < 2; _++) {
                if (tmp[0] <= tmp[1]) {
                    val += tmp[0];
                } else if (tmp[1] + p <= tmp[0]) {
                    val += tmp[1] + wait;
                } else {
                    double d = tmp[0] - tmp[1], prob = d / p;
                    // counter <= d -> 1, o.w. -> 0
                    val += (d / 2 + tmp[1]) * prob + tmp[0] * (1 - prob);
                }
                swap(tmp[0], tmp[1]);
            }
            val /= 2;
        }
    }

    auto ans = dp[0][0];
    cout << ans << '\n';
    return 0;
}