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

string to_string(string a) { return '"' + a + '"'; }
string to_string(char a) { return "'" + string(1, a) + "'"; }
string to_string(const char* a) { return to_string((string) a); }
string to_string(bool a) { return a ? "true" : "false"; }
template <class T1, class T2>
string to_string(pair<T1, T2> a) {
    return "(" + to_string(a.first) + ", " + to_string(a.second) + ")";
}
template <class T>
string to_string(T a) {
    bool first = true; string res = "{";
    for (const auto& i : a) {
        if (!first) res += ", ";
        first = false;
        res += to_string(i);
    }
    res += "}";
    return res;
}
void debug_out() { cerr << endl; }
template <class T1, class... T2>
void debug_out(T1 a, T2... b) {
    cerr << " " << to_string(a);
    debug_out(b...);
}

#ifdef LOCAL
#define out(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define out(...) 42
#endif

clock_t start_time; void start_timer() { start_time = clock(); }
double get_time() { return (double) (clock() - start_time) / CLOCKS_PER_SEC; }

void Solve();

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
#ifdef LOCAL
    freopen("../input.txt", "r", stdin);
#endif
    start_timer();
    Solve();
#ifdef LOCAL
    cerr << fixed << setprecision(3);
    cerr << endl << "Time spent: " << get_time() << endl;
#endif
    return 0;
}

typedef  double real_t;

real_t p;

real_t inter(real_t t1, real_t t2) {
    real_t q = t2 - t1;
    if (q < 0) {
        return t2;
    }
    q = min(q, p);
    return ((p - q) * t2 + q * t1 + q * q / 2) / p;
}

const int N = 1010;
const real_t INF = 1e15;

real_t dp[N][N];

void Solve() {
    int n, m;
    cin >> n >> m >> p;
    for (int i = 0; i < N; ++i) {
        dp[i][0] = INF;
        dp[0][i] = INF;
    }
    dp[1][1] = 0;
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= m; ++j) {
            double t1 = dp[i - 1][j];
            double t2 = dp[i][j - 1];
            if (i > 1 || j > 1) {
                dp[i][j] = 0.5 * (inter(t1, t2) + inter(t2, t1));
            }
        }
    }
    cout << fixed << setprecision(15) << dp[n][m] << '\n';
}