#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using LL = long long;
using pii = pair<int, int>;
#define sz(x) (signed)size(x)
#define db double
void solve () {
    int r, c;
    cin >> r >> c;
    db p;
    cin >> p;

    vector dp(r, vector<db>(c));
    for (int i = r - 1; i >= 0; i--) {
        for (int j = c - 1; j >= 0; j--) {
            if (i == r - 1 && j == c - 1) continue;
            if (i == r - 1) {
                dp[i][j] = p / 4 + dp[i][j + 1];
            } else if (j == c - 1) {
                dp[i][j] = p / 4 + dp[i + 1][j];
            } else {
                auto x = dp[i + 1][j], y = dp[i][j + 1];
                if (x > y) swap(x, y);
                if (x + p <= y) dp[i][j] = x + p / 4;
                else dp[i][j] = x / 2 + (p - y + x) / (2 * p) * y + (y - x) / (2 * p) * (x + (y - x) / 2);
            }
        }

    }

    cout << fixed << setprecision(10);
    cout << dp[0][0] << '\n';
}

signed main() {
    cin.tie(0)->sync_with_stdio(0);
    
    solve();
}