#define DINGER_GISBAR
//  {{{
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
//}}}
using namespace std;
const long long MOD = static_cast<int>(1e9) + 7;
//{{{TEMPLATE_BEGIN
typedef long long lint;
typedef unsigned long long ulint;
typedef long double ldouble;
typedef vector<int> vint;
#define rep(i, n) \
    for (int i = 0, i##_len = static_cast<int>(n); i < i##_len; i++)
#define all(c) begin(c), end(c)
#define perm(c)   \
    sort(all(c)); \
    for (bool c##p = 1; c##p; c##p = next_permutation(all(c)))
#define uniquenize(v) (v).erase(unique(all(v)), end(v))
#define cauto const auto &
#define memset(x, y) memset(x, y, sizeof(x))
#define popcount __builtin_popcount
#define gcd __gcd
inline lint bit(int x) { return 1LL << x; }
template <class T>
inline int size(const T& a) {
    return (int)a.size();
}
template <class T>
inline bool chmin(T& a, const T& b) {
    return a > b ? a = b, 1 : 0;
}
template <class T>
inline int clamp(T v, T lo, T hi) {
    return (v > hi) - (v < lo);
}
template <class T>
inline bool chmax(T& a, const T& b) {
    return a < b ? a = b, 1 : 0;
}
template <class T>
inline pair<vector<T>, char> operator*(const vector<T>& v, const char& c) {
    return make_pair(v, c);
}
template <class T>
inline istream& operator>>(istream& is, vector<T>& v) {
#ifdef ZEROKUGI
    if (v.empty()) {
        cerr << "Error L" << __LINE__ << ": vector size is zero." << endl;
        exit(EXIT_FAILURE);
    }
#endif
    for (auto& x : v) is >> x;
    return is;
}
template <class T>
inline ostream& operator<<(ostream& os, const pair<vector<T>, char>& v) {
    bool t = 0;
    for (const T& x : v.first) {
        if (t) os << v.second;
        os << x;
        t = 1;
    }
    return os;
}
template <class T>
inline ostream& operator<<(ostream& os, vector<T>& v) {
    return os << v * ' ';
}
struct before_main {
    before_main() {
        cin.tie(0);
        ios::sync_with_stdio(0);
        cout << fixed << setprecision(20);
    };
} __before_main;
//}}}TEMPLATE_END

int main() {
    lint n, m, d;
    cin >> n >> m >> d;


    lint c1 = min(n, 2*d);
    lint c2 = n - c1;
    if(d == 0) {
        c1 = n;
        c2 = 0;
    }
    ldouble ans = (c1 + c2 + c2 + 0.0) / n / n * (m-1);
    cout << ans << endl;
}


Measured memory_bytes: 384