#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> 
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long int
#define ld long double
#define pb push_back
#define pll pair<ll, ll> 
#define tri pair<pll, ll>
#define vl vector<ll> 
#define vvl vector< vector<ll> > 
#define vlp vector< pair<ll, ll> >
#define vllp vector<pair<pll, ll> > 
#define mll map<ll, ll> 
#define rep(i,a)  for(ll i=0; i< a; i++)
#define rep1(i,a)   for(ll i = 1; i< a; i++)
#define foi(i, a, b)    for(ll i = a; i<b ; i++)
#define fod(i, a, b)    for(ll i = a; i>=b ; i--)
#define mp make_pair
#define all(v)  (v).begin(), (v).end()
#define fst first
#define sec second
#define ff first.first
#define fs first.second
#define max3(a, b, c)   max(max(a, b), c)
#define min3(a, b, c)   min(min(a, b), c)
#define MAX 1000005
#define MOD 1000000007
// #define MOD 998244353
#define endl "\n"
#define INF (ll)1e18
#define s(v) (ll)v.size()
#define e(v) v.empty()
#define bscount(x) __builtin_popcountll(x)
// #define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>

using namespace std;
// using namespace __gnu_pbds;

ll gcd(ll a, ll b){if(b==0)return a;return gcd(b, a%b);}
ll cpow(ll a, ll b, ll M){ll ans = 1;while(b){if(b&1) ans = ans*a%M; b/=2;a=a*a%M;}return ans;}
void ingraph(vvl& graph, ll m){ll x, y;rep(i, m){cin>>x>>y;x--, y--;graph[x].pb(y);graph[y].pb(x);}}
ll modify(ll n){ll res = n;res%=MOD;res+=MOD;res%=MOD;return res;}
ll fexp(ll a, ll b) {return cpow(a, b, MOD);}
ll cinv(ll a, ll p){return cpow(a, p-2, p);} 
ll inverse(ll a)    {return cinv(a, MOD);}

int main(){
    // #ifndef ONLINE_JUDGE
    //     freopen("../input.txt", "r", stdin);
    //     freopen("../output.txt", "w", stdout);
    // #endif
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    ll t;
    // cin>>t;
    t = 1;
    ll tc = 0;
    while(tc++ < t){
    	ll n, m, d;
        cin>>n>>m>>d;
        ld ans = 1.0*(m-1)*(n-d)/(n*1.0*n);
        if(d > 0)	ans *= 2.0;
        cout<<fixed<<setprecision(10)<<ans;
    }
}
#include<bits/stdc++.h>
using namespace std;
#define FOR(i,l,r) for(long long i=(l);i<(r);++i)
#define REP(i,n) FOR(i,0,n)
#define REPS(i,n) FOR(i,1,n+1)
#define RFOR(i,l,r) for(long long i=(l);i>=(r);--i)
#define RREP(i,n) RFOR(i,n-1,0)
#define RREPS(i,n) RFOR(i,n,1)
#define int long long
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define SZ(x) ((int)(x).size())
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
template<class T> inline bool chmin(T& a, T b) {if (a > b) {a = b; return true; }return false; }
template<class T> inline bool chmax(T& a, T b) {if (a < b) {a = b; return true; }return false; }
const int INF = 1e18;

signed main(){
    double n, m, d; cin >> n >> m >> d;
    double ans = max(n-d,0.0)*(d !=0 ? 2 : 1) / (n*n) * (m-1);
    cout << fixed << setprecision(20.20) << ans << endl;
}