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 <iostream>
#include <string>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <unordered_map>
#include <map>
#include <set>
#include <algorithm>
#include <queue>
#include <stack>
#include <functional>
#include <bitset>
#include <assert.h>
#include <unordered_map>
#include <fstream>
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef pair<ll,ll> P;
typedef pair<int,int> pii;
typedef vector<P> vpl;
typedef tuple<ll,ll,ll> tapu;
#define rep(i,n) for(int i=0; i<(n); i++)
#define REP(i,a,b) for(int i=(a); i<(b); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
const int inf = 1<<30;
const ll linf = 1LL<<62;
const int MAX = 510000;
ll dy[8] = {0,-1,0,1,1,-1,1,-1};
ll dx[8] = {1,0,-1,0,1,-1,-1,1};
const double pi = acos(-1);
const double eps = 1e-7;
template<typename T1,typename T2> inline bool chmin(T1 &a,T2 b){
	if(a>b){
		a = b; return true;
	}
	else return false;
}
template<typename T1,typename T2> inline bool chmax(T1 &a,T2 b){
	if(a<b){
		a = b; return true;
	}
	else return false;
}
template<typename T> inline void print(T &a){
    rep(i,a.size()) cout << a[i] << " ";
    cout << "\n";
}
template<typename T1,typename T2> inline void print2(T1 a, T2 b){cout << a << " " << b << "\n";}
template<typename T1,typename T2,typename T3> inline void print3(T1 a, T2 b, T3 c){
	cout << a << " " << b << " " << c << "\n";
}
const ll mod = 1e9 + 7;
//const int mod = 998244353;

int main(){
    while(1){
        int n,m,K; cin >> n >> m >> K;
        if(n+m+K == 0) break;
        double ans = 0.0;
        vector<vd> dp(n+1,vd(n*m+1,0.0));
        dp[0][0] = 1.0;
        rep(i,n){
            rep(j,n*m){
                REP(k,1,m+1){
                    if(j+k <= n*m) dp[i+1][j+k] += dp[i][j] / (double)m;
                }
            }
        }
        rep(i,n*m+1){
            double t = i-K;
            ans += max(t,1.0) * dp[n][i];
        }
        printf("%.10f\n",ans);
    }
}

C++: #include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <climits>
#include <vector>
#include <map>
#include <set>
#include <list>
#include <stack>
#include <queue>
#include <algorithm>
#include <iostream>
#include <string>

#define REP(i,n) for(long long i=0;i<n;++i)
#define REPR(i,n) for(long long i=n;i>=0;--i)
#define REPI(itr,v) for(auto itr=v.begin();itr!=v.end();++itr)
#define REPIR(itr,v) for(auto itr=v.rbegin();itr!=v.rend();++itr)
#define FOR(i,a,b) for(long long i=a;i<b;++i)
#define SORT(v,n) sort(v, v+n)
#define SORTV(v) sort(v.begin(), v.end())
#define ALL(v) v.begin(),v.end()
#define llong long long
#define INF 999999999
#define SUR 1000000007
#define pb push_back
#define pf push_front
#define MP make_pair
#define SV(v) {for(long long sitr=0;sitr<v.size();++sitr){cin>>v[sitr];}}

int dx[] = {0, 0, -1, 1};
int dy[] = {1, -1, 0, 0};

using namespace std;

typedef pair<int,int> pii;

int main(){

  while(true){
    vector<vector<llong>> dp;
    llong n, m, k;
    scanf("%lld %lld %lld", &n, &m, &k);
    
    if(n == 0 && m == 0 && k == 0) break;

    dp = vector<vector<llong>>(n+1, vector<llong>(n * m+1, 0));
    dp[0][0] = 1;
    for(int i = 0; i < n; ++i){
      for(int j = 0; j <= n * m; ++j){
        for(int k = 1; k <= m; ++k){
          if(j + k <= n * m){
            dp[i+1][j+k] += dp[i][j];
          }
        }
      }
    }
    double p = 1.0;
    REP(i, n){
      p /= m;
    }
    double ans = 0.0;
    REP(i,n*m+1){
      double bill;
      if(i <= k){
        bill = 1;
      }else{
        bill = i - k;
      }
      //cout << dp[n][i] << " " << bill << " " << p << endl; 
      ans += (double)dp[n][i] * bill * p;
      //cout <<  i << " " << dp[n][i] * p << " " << dp[n][i] * bill * p << endl;
    }

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

  }

  return 0;
}