#include<bits/stdc++.h>
using namespace std;
int main(){
    int n, k;
    double f, fac[105];
    cin >> f >> n >> k;
    fac[0] = 1;
    for(int i = 1; i < 105; i++) fac[i] = fac[i - 1] * i;
    double ans = 0;
    for(int i = 1; i <= f; i++){
        double sum = 0;
        double A = (i - 1) / f;
        double B = 1 / f;
        double C = (f - i) / f;
        for(int x = 0; x < n - k + 1; x++)
            for(int y = 0; y < k; y++)
                sum += pow(A, x) * pow(B, n - x - y) * pow(C, y) * (fac[n] / fac[x] / fac[y] / fac[n - x - y]);
        ans += i * sum;
    }
    printf("%.7f\n", ans);
    return 0;
}