#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int, int>
#define fr first
#define sc second
inline int rd() {
    int f = 1, tmp = 0;
    char ch = getchar();
    while (!isdigit(ch)) {
        if (ch == '-')
            f = -1;
        ch = getchar();
    }
    while (isdigit(ch)) {
        tmp = tmp * 10 + (ch - '0');
        ch = getchar();
    }
    return tmp * f;
}
const int N = 510;
double f[N][N], C[N][N], g[N][N];
int n, d, r;
signed main() {
    n = rd();
    d = rd();
    r = rd();
    C[0][0] = 1;
    for (int i = 1; i <= n; i++) {
        C[i][0] = 1;
        for (int j = 1; j <= i; j++) {
            C[i][j] = C[i - 1][j - 1] + C[i - 1][j];
        }
    }
    f[0][n] = 1;
    for (int i = 0; i < d; i++) {
        for (int j = 1; j <= n; j++) {
            for (int k = 1; k <= j; k++) {
                f[i + k][k] += f[i][j] * C[j][k];
                g[i + k][k] += (g[i][j] + f[i][j] * min(k, r)) * C[j][k];
            }
        }
    }
    double ans1 = 0, ans2 = 0;
    for (int i = 1; i <= n; i++) {
        ans1 += g[d][i];
        ans2 += f[d][i];
    }
    printf("%.6lf", ans1 / ans2 + r);
    return 0;
}