#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ldb;
typedef pair<int, int> pii;
const int MAXN = 500 + 5;

const int MAXF = MAXN * 2;
ldb C[MAXF][MAXF];

int main(void) {
    int n, d, r;
    scanf("%d%d%d", &n, &d, &r);

    for (int i = 0; i <= n + d; ++i) {
        C[i][0] = 1;

        for (int j = 1; j <= i; ++j)
            C[i][j] = C[i - 1][j] + C[i - 1][j - 1];
    }

    ldb ans = 0;

    for (int i = 1; i <= d; ++i) {
        static ldb f[MAXN][MAXN];
        f[0][0] = 1;

        for (int j = 1; j <= n; ++j) {
            ldb cur = 0;

            for (int k = 0; k <= d; ++k) {
                cur += f[j - 1][k];

                if (k - i >= 0)
                    cur -= f[j - 1][k - i];

                f[j][k] = cur;
            }
        }

        for (int j = 1; j <= n && i * j <= d; ++j)
            for (int k = 0; i * j + k <= d; ++k)
                ans += f[n - j][d - i * j - k] * C[k + j - 1][j - 1] * C[n][j] * min(r, j);
    }

    for (int i = 1; i <= d; ++i)
        ans = ans * i / (n + i - 1);

    ans += r;
    printf("%.20lf", (double)ans);
    return 0;
}