Go: package main

import (
	"fmt"
	"math"
)

func main(){
	var n, m, k int
	for {
		fmt.Scan(&n, &m, &k)
		if n == 0 && m == 0 && k == 0{
			break
		}

		dp := make([][]int, n+1)
		for i:= 0; i < n+1; i++{
			dp[i] = make([]int, m*n + 1)
		}

		for i := 1; i <=m ; i++{
			dp[1][i] = 1
		}

		for i:= 1; i < n; i++{
			for j := 0; j <= i * m; j++{
				for k := 1; k <= m; k++{
					dp[i+1][j+k] += dp[i][j]
				}
			}
		}

		count := 0.0
		div := math.Pow(float64(m), float64(n))
		for i := 0; i <= n * m; i++{
			bill := 0.0
			if i <= k{
				bill = 1.0
			} else {
				bill = float64(i - k)
			}
			count += bill * float64(dp[n][i]) / div
		}
		fmt.Printf("%.010f\n", count)
	}
}

C++: ////////////////////////////////////////
///  tu3 pro-con template            ///
////////////////////////////////////////
#include <cassert>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <algorithm>
#include <numeric>
#include <functional>
#include <vector>
#include <queue>
#include <string>
#include <complex>
#include <stack>
#include <set>
#include <map>
#include <list>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <regex>
#include <type_traits>
#include <mutex>
#include <array>
using namespace std;

//// MACRO ////
#define countof(a) (sizeof(a)/sizeof(a[0]))

#define REP(i,n) for (int i = 0; i < (n); i++)
#define RREP(i,n) for (int i = (n)-1; i >= 0; i--)
#define FOR(i,s,n) for (int i = (s); i < (n); i++)
#define RFOR(i,s,n) for (int i = (n)-1; i >= (s); i--)
#define pos(c,i) c.being() + (i)
#define allof(c) c.begin(), c.end()
#define aallof(a) a, countof(a)
#define partof(c,i,n) c.begin() + (i), c.begin() + (i) + (n)
#define apartof(a,i,n) a + (i), a + (i) + (n)
typedef unsigned int uint;
typedef long long llong;
typedef unsigned long long ullong;
#define long long long

#define EPS 1e-9
#define INF (1L << 28)
#define LINF (1LL << 60)

#define PREDICATE(t,a,exp) [&](const t & a) -> bool { return exp; }
#define COMPARISON_T(t) bool(*)(const t &, const t &)
#define COMPARISON(t,a,b,exp) [&](const t & a, const t & b) -> bool { return exp; }
#define CONVERTER(TSrc,t,TDest,exp) [&](const TSrc &t)->TDest { return exp; }

#define PRED(a,exp) [&](const auto & a) -> bool { return exp; }
#define COMP(a,b,exp) [&](const auto & a, const auto & b) -> bool { return exp; }

inline int sign_of(double x) { return abs(x) < EPS ? 0 : x > 0 ? 1 : -1; }
inline bool inRange(int val, int min, int max) { return val >= min && val < max; }
inline bool inRange(double val, double min, double max) { return val - min > -EPS && val - max < EPS; }
inline bool inRange(int x, int y, int W, int H) { return x >= 0 && x < W && y >= 0 && y < H; } // W,H含まない

template <class T> struct vevector : public vector<vector<T>> { vevector(int n = 0, int m = 0, const T &initial = T()) : vector<vector<T>>(n, vector<T>(m, initial)) { } };
template <class T> struct vevevector : public vector<vevector<T>> { vevevector(int n = 0, int m = 0, int l = 0, const T &initial = T()) : vector<vevector<T>>(n, vevector<T>(m, l, initial)) { } };
template <class T> struct vevevevector : public vector<vevevector<T>> { vevevevector(int n = 0, int m = 0, int l = 0, int k = 0, const T &initial = T()) : vector<vevevector<T>>(n, vevevector<T>(m, l, k, initial)) { } };

//// i/o helper ////

namespace std {
	template <class T1, class T2> inline istream & operator >> (istream & in, pair<T1, T2> &p) { in >> p.first >> p.second; return in; }
	template <class T1, class T2> inline ostream & operator << (ostream &out, const pair<T1, T2> &p) { out << p.first << " " << p.second; return out; }
}
template <class T> T read() { T t; cin >> t; return t; }
template <class T> vector<T> read(int n) { vector<T> v; v.reserve(n); REP(i, n) { v.push_back(read<T>()); } return v; }
template <class T> vevector<T> read(int n, int m) { vevector<T> v; REP(i, n) v.push_back(read<T>(m)); return v; }
template <class T> vector<T> readjag() { return read<T>(read<int>()); }
template <class T> vevector<T> readjag(int n) { vevector<T> v; v.reserve(n); REP(i, n) v.push_back(readjag<T>()); return v; }

template <class T> struct iter_pair_t { T beg, end; };
template <class T> iter_pair_t<T> iter_pair(T beg, T end) { return iter_pair_t<T>{beg, end}; }
template <class T> ostream & operator << (ostream &out, const iter_pair_t<T> &v)
{
	std::copy(v.beg, v.end, ostream_iterator<typename decltype(v.beg)::reference>(out, " "));
	return out;
}
template <class T1> ostream & operator << (ostream &out, const vector<T1> &v) { return out << iter_pair(begin(v), end(v)); }
template <class T1> ostream & operator << (ostream &out, const set<T1> &v) { return out << iter_pair(begin(v), end(v)); }
template <class T1, class T2> ostream & operator << (ostream &out, const map<T1, T2> &v) { return out << iter_pair(begin(v), end(v)); }

struct _Reader { istream &cin; template <class T> _Reader operator ,(T &rhs) { cin >> rhs; return *this; } };
struct _Writer { ostream &cout; bool f{ false }; template <class T> _Writer operator ,(const T &rhs) { cout << (f ? " " : "") << rhs; f = true; return *this; } };
#define READ(t,...) t __VA_ARGS__; (_Reader{cin}), __VA_ARGS__
#define WRITE(...) (_Writer{cout}), __VA_ARGS__; cout << '\n'
#define DEBUG(...) (_Writer{cerr}), __VA_ARGS__; cerr << '\n'

void solve();
int main()
{
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);

	//auto temp = ctype<char>::classic_table();
	//vector<ctype<char>::mask> bar(temp, temp + ctype<char>::table_size);
	//bar[':'] |= ctype_base::space;
	//cin.imbue(locale(cin.getloc(), new ctype<char>(bar.data())));

	cin.tie(0);
	ios_base::sync_with_stdio(false);
	cout << fixed;
	cout << setprecision(std::numeric_limits<double>::max_digits10);
	solve();

	return 0;
}

/// サイコロの出目の合計値の確率
// retval[n] = 等確率に出目が出るサイコロ xi を N 回振って出目の合計値が n となる確率
vector<double> xicolo_sum_prob(
	int N,
	const vector<int> &xi = vector<int>{ 1, 2, 3, 4, 5, 6 },
	const vector<double> &initial = vector<double>(1, 1))
{
	int maxN = *max_element(allof(xi));
	auto dp = initial;
	REP(i, N)
	{
		vector<double> next(dp.size() + maxN);
		REP(i, dp.size())
		{
			for (auto x : xi)
			{
				next[i + x] += dp[i] / xi.size();
			}
		}
		dp.swap(next);
	}
	return dp;
}

////////////////////
/// template end ///
////////////////////

void solve()
{
	while (true)
	{
		READ(int, n, m, k);
		if (!n) { break; }
		vector<int> xi(m);
		iota(allof(xi), 1);
		auto prob = xicolo_sum_prob(n, xi);

		double expect = 0.0;

		REP(i, prob.size())
		{
			if (i <= k) { expect += prob[i]; }
			else { expect += prob[i] * (i - k); }
		}

		WRITE(expect);
	}


}

C++: #include <iostream>
#include <cmath>
#include <cstring>
#include <cstdio>

using namespace std;

const int MAX_N = 1e6;
int n, m, k;
int cnt[MAX_N];

void Rec(int idx, int sum)
{
    if (idx >= n) {
        if (sum - k <= 1)
            ++cnt[1];
        else
            ++cnt[sum - k];

        return ;
    }

    for (int i = 1; i <= m; ++i)
        Rec(idx + 1, sum + i);
}

int main()
{
    while (cin >> n >> m >> k, n) {
        int sum = pow(m, n);

        memset(cnt, 0, sizeof(cnt));

        Rec(0, 0);

        double ans = 0.0;
        for (int i = 1; i <= n * m - k; ++i)
            ans += i * (double)cnt[i] / sum;

        printf("%.8f\n", ans);
    }

    return 0;
}

C++: #include <iostream>
#include <cmath>

using namespace std;

int n, m, k, x;
double ans;

void dfs(int node, int sum) {
    if (node == n) {
        if (sum-k < 1) sum = 1;
        else sum -= k;
        ans += (double)sum / x;
        return;
    }
    for (int i = 1; i < m+1; i++) {
        dfs(node+1, sum+i);
    }
    return;
}

int main(void){
    while (cin>>n>>m>>k && n) {
        ans = 0;
        x = pow(m,n);
        dfs(0, 0);
        printf("%.12lf\n",ans);
    }
}