#include <bits/stdc++.h>

using namespace std;
using db = double;

const int N = 1010;

int n, m, p;
db dp[N][N];

int main() {
    ios::sync_with_stdio(0), cin.tie(0);
    cin >> n >> m >> p;
    for (int i = n; i >= 1; i--) {
        for (int j = m - (i == n); j >= 1; j--) {
            if (i == n) dp[i][j] = dp[i][j + 1] + p / 4.0;
            else if (j == m) dp[i][j] = dp[i + 1][j] + p / 4.0;
            else {
                db x = dp[i][j + 1], y = dp[i + 1][j];
                if (x > y) swap(x, y);
                db tp = min(y - x, (db)p);  // t <= tp : x  t > tp : y
                dp[i][j] = x / 2 + ((x + tp / 2) * tp + y * (p - tp)) / p / 2;
            }
        }
    }
    cout << fixed << setprecision(8) << dp[1][1];
    return 0;
}

/*
sum = (p + 1) * p / 2
val = sum / (p + 1) = p / 2
*/