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

#define rep(i,n) for(long long i = 0; i < (long long)(n); i++)
using ll = long long; using ld = double;
#define ldout fixed << setprecision(40) 

int main(void) {
    ll f, n, k; cin >> f >> n >> k;
    ld ret = 0;
    vector<ld> fact(200); fact[0] = 1; rep(i, fact.size()) fact[i+1] = fact[i] * (i + 1);

    rep(i, f) {
        ld s = 0;
        rep(j, n) rep(h, n) if (j <= n - k && n - k <= n - h - 1) 
            s += (ld)1 * (fact[n] / fact[j] / fact[h] / fact[n-j-h]) * powl(i, j) * powl(f-i-1, h);
        ret += (i+1) * s;
    }

    cout << ldout << ret / pow(f, n) << endl;
    
    return 0;
}