#include <bits/stdc++.h>
using namespace std;

const int N = 2000;

int n, m;
long double dp[N][N], p;

long double calc(long double x, long double y) {
    //x < y + t
    //t > x - y
    long double h = x - y;
    if (h <= 0.0) {
        return x;
    }
    if (h >= p)
        return y + p / 2.0;
    return (y * h + (h * h) / 2 + x * (p - h)) / p;
}

int main() {
    ios_base::sync_with_stdio(0), cin.tie(0);
    cin >> n >> m >> p;
    dp[0][0] = 0;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            if (i == 0 && j == 0) continue;
            if (i == 0) {
                dp[i][j] = dp[i][j - 1] + p/4.0;
                continue;
            }
            if (j == 0) {
                dp[i][j] = dp[i - 1][j] + p/4.0;
                continue;
            }
            long double x = dp[i - 1][j], y = dp[i][j - 1];
            dp[i][j] = (calc(x, y) + calc(y, x)) / 2.0;
        }
    }
    cout << fixed << setprecision(9) << dp[n - 1][m - 1] << '\n';
}