#include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define o(a) cout << a << endl
// #define int long long
#define first fi
#define second se
using namespace std;
typedef pair<int, int> P;

int d[30][300010];

signed main(){
    int n, m, k;
    while(1){
        cin >> n >> m >> k;
        if(n + m + k == 0) break;
        rep(i, 0, 30) rep(j, 0, 300010) d[i][j] = 0;
        d[0][0] = 1;
        rep(i, 0, n){
            rep(j, i, 300000){
                if(d[i][j] == 0) break;                
                rep(l, 1, m + 1){
                    d[i + 1][j + l] += d[i][j];
                }
            }
        }
        double sum = 0;
        rep(i, 0, 300000){
            if(i <= k) sum += d[n][i];
            else sum += d[n][i] * (i - k);
        }
        rep(i, 0, n) sum /= (double)m;
        printf("%.14lf\n", sum);
    }
}