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

typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> ii;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<ii> vii;

#define x first
#define y second
#define pb push_back
#define eb emplace_back
#define rep(i,a,b) for(auto i=(a); i<(b); ++i)
#define REP(i,n) rep(i,0,n)
#define all(v) begin(v), end(v)
#define sz(v) ((int) (v).size())
#define rs resize
#define DBG(x) cerr << __LINE__ << ": " \
		<< #x<< " = " << (x) << endl

template<class T> ostream& operator<<(ostream &os,
		const vector<T> &v) {
	os << "\n[";
	for(const T &x : v) os << x << ',';
	return os << "]\n";
}

namespace std { template<class T1, class T2>
struct hash<pair<T1,T2>> { public:
	size_t operator()(const pair<T1,T2> &p) const {
		size_t x = hash<T1>()(p.x), y = hash<T2>()(p.y);
		return x ^ (y + 0x9e3779b9 + (x<<6) + (x>>2));
	}
}; }

void run() {
	ll n, i, k;
	cin >> n >> i >> k;
	i--;
	vector<ld> B(n, 0);
	ld s = ((ld) 1)/n;
	B[0] = s;
	for (ll j = n-1; j >= 1; j--) {
		ld g = 0;
		if (i == j) g = 1;
		ld a = (s-g)/j;
		B[j] = a;
		s += a;
	}
	ld res = ((ld) n+1)/2;
	for (ll j = 1; j < n; j++) {
		res -= B[j] * j*(j+1)/2 * pow(((ld)j)/n, k);
	}
	cout << res << endl;

}

signed main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout << fixed << setprecision(20);
	run();
	return 0;
}