/*#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>

#include <boost/rational.hpp>
*/
#include <bits/stdc++.h>
using namespace std;
#define _GLIBCXX_DEBUG
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
using ll = long long;
using ld = long double;
#define rep2(i, s, n) for (ll i = (s); i < (ll)(n); i++)
#define rep3(i, n) for (ll i = 1; i < (ll)(n+1); i++)
#define rep4(i, s, n) for (ll i = (s); i < (ll)(n+1); i++)
#define repr(i,n) for (ll i = (n-1); i>=0;i--)
#define repr3(i,n) for(ll i = (n);i>0;i--)
#define repr4(i,s,n) for(ll i = (n);i>=(s);i--)
#define stlen(s) ll s.size()-1
#define all(v) v.begin(), v.end()
#define allr(v) v.rbegin(), v.rend()
#define cout(n) cout<<std::fixed<<std::setprecision(n)
using Graph = vector<vector<int>>;
using Graphw = vector<vector<pair<ll,ll>>>;
#define INF1  INT_MAX;
#define INF2  LLONG_MAX;
#define PI  3.14159265358979323846;
#define MOD 1000000007;
/*
namespace mp = boost::multiprecision;
// 任意長整数型
using Bint = mp::cpp_int;
// 仮数部長が32の浮動小数点数型
using Real32 = mp::number<mp::cpp_dec_float<32>>;
// 仮数部長が1024の浮動小数点数型
using Real1024 = mp::number<mp::cpp_dec_float<1024>>;
// 有理数型
using Rat = boost::rational<Bint>;
*/
const int mod = 1000000007;

template <class T>
bool chmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return 1;
    }
    return 0;
}

int main(){
ll n,m,d;
cin>>n>>m>>d;
if(d==0){
    cout<<(ld)(m-1)/n<<endl;
}
else{
    cout(10)<<(ld)2*(n-d)*(m-1)/(n*n)<<endl;
}
return 0;
}
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<vector>
#include<functional>
#include<algorithm>
#include<stdlib.h>
#include<string>
#include<string.h>
#define _USE_MATH_DEFINES
#include<math.h>
#include<deque>
#include<set>
#include<map>
#include<queue>
#include<list>
#include<iostream>
using namespace std;
typedef long long ll;
#define rep(i,a,b) for(auto i=a;i<b;i++)
#define all(_x) _x.begin(), _x.end()
#define r_sort(_x) sort(_x.begin(), _x.end(), std::greater<int>())
#define vec_cnt(_a, _n) (upper_bound(all(_a), _n) - lower_bound(all(_a), _n))
ll gcd(ll a, ll b) { return a % b == 0 ? b : gcd(b, a % b); }
//ll lcm(ll a, ll b) { return (a / gcd(a, b)) * b; }
#define INF 1 << 30
const int mod = 1000000007;
int main() {
	double n, m, d;
	cin >> n >> m >> d;
	printf("%f\n", (n - d) / n / n * (d == 0 ? 1 : 2) * (m - 1));
	return 0;
}
