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

const int INF = 1000000007;
const int MOD = 1000000007;

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

int main(){
    int n, m, k;
    while(true){
        scanf("%d%d%d", &n, &m, &k);
        if((n|m|k) == 0) break;
        vector<double> ep(n * m + 1);
        fill(ep.begin(), ep.end(), 0);
        ep[0] = 1;
        for(int i = 0; i < n; ++i){
            for(int j = m * i; j >= 0; --j){
                for(int l = 1; l <= m; ++l){
                    if(j + l > n * m) break;
                    ep[j + l] += ep[j] / m;
                }
                ep[j] = 0;
            }
        }
        double ans = 0;
        for(int i = 0; i <= n * m; ++i){
            ans += max(i - k, 1) * ep[i];
        }
        printf("%.12f\n", ans);
        ep.clear();
    }
    
    return 0;
}