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++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <ctime>
#include <cassert>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <numeric>
#include <list>
#include <iomanip>
#include <fstream>
#include <bitset>
   
using namespace std;
   
 
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define foreach(it, c) for (__typeof__((c).begin()) it=(c).begin(); it != (c).end(); ++it)
#define rforeach(it, c) for (__typeof__((c).rbegin()) it=(c).rbegin(); it != (c).rend(); ++it)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define CL(arr, val) memset(arr, val, sizeof(arr))
#define COPY(dest, src) memcpy(dest, src, sizeof(dest))
#define ten(n) ((long long)(1e##n))
#define bin(n) (1LL << (n))
#define erep(i, n) for (int i = 0; i <= (int)(n); ++i)
#define revrep(i, n) for (int i = (n); i >= 0; --i)
#define pb push_back

template <class T> void chmax(T& a, const T& b) { a = max(a, b); }
template <class T> void chmin(T& a, const T& b) { a = min(a, b); }

template <class T> void uniq(T& c) { sort(c.begin(), c.end()); c.erase(unique(c.begin(), c.end()), c.end()); }
 
template <class T> string to_s(const T& a) { ostringstream os; os << a; return os.str(); }
template <class T> T to_T(const string& s) { istringstream is(s); T res; is >> res; return res; }

template <typename T> void print_container(ostream& os, const T& c) { const char* _s = " "; if (!c.empty()) { __typeof__(c.begin()) last = --c.end(); foreach (it, c) { os << *it; if (it != last) cout << _s; } } }
template <typename T> ostream& operator<<(ostream& os, const vector<T>& c) { print_container(os, c); return os; }
template <typename T> ostream& operator<<(ostream& os, const set<T>& c) { print_container(os, c); return os; }
template <typename T> ostream& operator<<(ostream& os, const multiset<T>& c) { print_container(os, c); return os; }
template <typename T> ostream& operator<<(ostream& os, const deque<T>& c) { print_container(os, c); return os; }
template <typename T, typename U> ostream& operator<<(ostream& os, const map<T, U>& c) { print_container(os, c); return os; }
template <typename T, typename U> ostream& operator<<(ostream& os, const pair<T, U>& p) { os << "( " << p.first << ", " << p.second << " )"; return os; }

template <class T> void print(T a, int n, const string& deli = " ", int br = 1) { for (int i = 0; i < n; ++i) { cout << a[i]; if (i + 1 != n) cout << deli; } while (br--) cout << endl; }
template <class T> void print2d(T a, int w, int h, int width = -1, int br = 1) { for (int i = 0; i < h; ++i) { for (int j = 0; j < w; ++j) {    if (width != -1) cout.width(width); cout << a[i][j] << ' '; } cout << endl; } while (br--) cout << endl; }

template <class T> void input(T& a, int n) { for (int i = 0; i < n; ++i) cin >> a[i]; }
template <class T> void input(T* a, int n) { for (int i = 0; i < n; ++i) cin >> a[i]; }

void fix_pre(int n) { cout.setf(ios::fixed, ios::floatfield); cout.precision(10); }
void fast_io() { cin.tie(0); ios::sync_with_stdio(false); }
#define trace(x) (cout << #x << ": " << (x) << endl)
 
bool in_rect(int x, int y, int w, int h) { return 0 <= x && x < w && 0 <= y && y < h; }
bool in_seg(int n, int l, int r) { return l <= n && n < r; } // n in [l, r)?

typedef long long ll;
typedef pair<int, int> pint;

// y(v): v>^<  y(^): ^>v<
const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { 1, 0, -1, 0 };

const double PI = acos(-1.0);
#define mp make_pair



int main()
{
    int n, m, k;
    while (scanf("%d%d%d", &n, &m, &k), n)
    {
        double dp[40][ten(4) + 100];
        erep(i, n) erep(j, m * i)
            dp[i][j] = 0;

        dp[0][0] = 1;
        rep(i, n)
        {
            for (int j = i; j <= m * i; ++j)
            {
                double p = dp[i][j] / m;
                for (int nj = j + 1, u = min(j + m, m * i + m); nj <= u; ++nj)
                    dp[i + 1][nj] += p;
            }
        }
        
        double res = 0;
        erep(j, n * m)
            res += max(1, j - k) * dp[n][j];
        printf("%.8f\n", res);
    }
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <ctype.h>
#include <string> 
#include <cstring>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <queue>
#include <utility>
#include <vector>
#include <set>
#include <iomanip>
#include <stack>
   
using namespace std;
 
#define pi 3.141592653589793
 
int main()
{
    int n, m, k;
    while(1){
        cin >> n >> m >> k;
        if(n == 0 && m == 0 && k == 0) break;
        double result[n * m + 1][n + 1];
        for(int i = 0; i < n * m + 1; i++){
            for(int j = 0; j < n + 1; j++){
                result[i][j] = 0.0;
            }
        }
        for(int i = 1; i < m + 1; i++){
            result[i][1] = (double)1 / m;
        }
        for(int i = 2; i < n + 1; i++){
            for(int j = 1; j < m * (i - 1) + 1; j++){
                for(int k = 1; k < m + 1; k++){
                    result[j + k][i] += (double)result[j][i - 1] / m;
                }
            }
        }
        double ans = 0;
        for(int i = 1; i < n * m + 1; i++){
            if(i > k){
                ans += (i - k) * result[i][n];
            } else {
                ans += result[i][n];
            }
        }
        printf("%15.10f\n", ans);
    }
    return 0;
}

C++: #include<iostream>
#include<string>
#include<vector>
#include<cstdio>
#include<sstream>
#include<algorithm>
#include<cmath>
#include<map>
#include<functional>
#include<queue>
#include<stack>
#include<set>
using namespace std;
#define SZ(n)  (int)n.size()
#define dump(x) cerr<<#x<<" = "<<(x)<<endl;
#define debug(x)cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#define MP make_pair
#define PB push_back
const int INF=1<<28;
	int n,m,k;
	int p[300000];
	void dfs(int now,int sum){
		if(now==n)p[sum]++;
		if(now==n)return ;
		for(int i=1;i<=m;i++)dfs(now+1,sum+i);
	}
	
	int main(){
	while(cin>>n>>m>>k,n+m+k){
	dfs(0,0);
	double ans=0.0;
	int kaku=pow(m,n);
	for(int i=1;i<=m*n;i++){
		double a=(double)p[i]/double(kaku);
		double b=max(double(i-k),1.0);
		ans+= a*b;
	}
	printf("%.10lf\n",ans);
	fill(p,p+300000,0);
	}
	return 0;
}