#include <bits/stdc++.h>
#define int long long

using namespace std;

void solve () {
    int n, m, p;
    cin >> n >> m >> p;

    const double Z = 0.25 * p;

    vector dp (n + 1, vector <double> (m + 1));
    for (int i = n; i >= 1; i --) {
        for (int j = m; j >= 1; j --) {
            if (i == n && j == m) {
                dp[i][j] = 0;
            } else if (i == n) {
                dp[i][j] = dp[i][j + 1] + Z;
            } else if (j == m) {
                dp[i][j] = dp[i + 1][j] + Z;
            } else {
                double a = dp[i][j + 1], b = dp[i + 1][j];
                if (a > b) {
                    swap (a, b);
                }
                if (b - a >= p) {
                    dp[i][j] = a + Z;
                } else {
                    dp[i][j] = a * 0.5 + ((b - a) / p * (a + (b - a) * 0.5) + (p - (b - a)) / p * b) * 0.5;
                }
            }
        }
    }

    cout << dp[1][1] << '\n';
}

signed main () {
    ios::sync_with_stdio (false);
    cin.tie (nullptr);

    cout << fixed << setprecision (10);

    int T = 1;
    // cin >> T;

    while (T --) {
        solve ();
    }

    return 0;
}