#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)

using namespace std;
using ll = long long;

int main() {
    int f, n, k;
    cin >> f >> n >> k;
    
    vector c(n+1, vector<double>(n+1));
    c[0][0] = 1;
    rep(i, n)rep(j, i+1) {
        c[i+1][j] += c[i][j];
        c[i+1][j+1] += c[i][j];
    }
    
    double ans = 0;
    for (int i = 1; i <= f; ++i) {
        double now = 0;
        for (int j = k; j <= n; ++j) {
            now += c[n][j]*pow(f-i+1, j)*pow(i-1, n-j);
        }
        ans += now;
    }
    ans /= pow(f, n);
    
    printf("%.10f\n", ans);
     
    return 0;
}