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

using i64 = long long;

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    int r, c, p;
    cin >> r >> c >> p;
    vector<vector<double>> f(r, vector<double>(c));
    for(int i = r - 1; i >= 0; i--) {
        for(int j = c - 1; j >= 0; j--) {
            double a = -1, b = -1;
            if(i + 1 < r) {
                a = f[i + 1][j];
            }
            if(j + 1 < c) {
                b = f[i][j + 1];
            }
            if(a > b) swap(a, b);
            if(b == -1) continue;
            if(a == -1) {
                f[i][j] = b + p / 4.;
            } else if(b >= a + p) {
                f[i][j] = a + p / 4.;
            } else {
                f[i][j] = (p - (b - a)) / 2. / p * b + a / 2. + (b - a) / 2. / p * (a + b) / 2;
            }
        }
    }
    cout << setprecision(20) << f[0][0] << '\n';
    return 0;
}