#include <bits/stdc++.h>
using namespace std;
typedef long long lint;
#define rep(i,n) for(lint (i)=0;(i)<(n);(i)++)
#define repp(i,m,n) for(lint (i)=(m);(i)<(n);(i)++)
#define repm(i,n) for(lint (i)=(n-1);(i)>=0;(i)--)
#define INF (1ll<<60)
#define all(x) (x).begin(),(x).end()
const lint MOD =1000000007;
const lint MAX = 1000000;
using Graph =vector<vector<lint>>;
typedef pair<lint,lint> P;
 
 
lint fac[MAX], finv[MAX], inv[MAX];
 
void COMinit() 
{
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (lint i = 2; i < MAX; i++)
    {
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}
 
long long COM(lint n, lint k)
{
    if (n < k)
        return 0;
    if (n < 0 || k < 0)
        return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
 
lint primary(lint num)
{
    if (num < 2) return 0;
    else if (num == 2) return 1;
    else if (num % 2 == 0) return 0;
 
    double sqrtNum = sqrt(num);
    for (int i = 3; i <= sqrtNum; i += 2)
    {
        if (num % i == 0)
        {
            return 0;
        }
    }
 
    return 1;
}
   long long modpow(long long a, long long n, long long mod) {
    long long res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % mod;
        a = a * a % mod;
        n >>= 1;
    }
    return res;
}
    lint lcm(lint a,lint b){
        return a/__gcd(a,b)*b;
    }
     lint gcd(lint a,lint b){
        return __gcd(a,b);
    } 
 ///解説AC
  int main(){      
      double n,m,d;
      cin>>n>>m>>d;
      if(d==0){
          printf("%.9f",1/n*(m-1));
      }else{
          printf("%.9f",2*(n-d)/n/n*(m-1));
      }
      }
      
    

  
          
  
//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define all(v) v.begin(), v.end()
using in = int64_t;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define REP(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define Yes cout<<"Yes"<<endl
#define No cout<<"No"<<endl
#define yes cout<<"yes"<<endl
#define no cout<<"no"<<endl
const double PI=3.14159265358979323846;
const in MOD = 1000000007;
const in INF=1e18+7;
const int inf=1e9+7;
using P=pair<int,int>;
vector<int> dx={0,1,-1,0};
vector<int> dy={1,0,0,-1};

using ld=long double;

int main(){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cout << fixed << setprecision(10);
    ld n,m,d;
    cin>>n>>m>>d;
    ld ans=(m-1.0)*(n-d);
    if(d!=0.0) ans *=2.0;
    ans /=n;
    ans /=n;
    cout<<ans<<'\n';
}/*
./problem.exe
*/