#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;
}
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(k,i,n) for(ll i=k;i<n;++i)
int main(void){
    ll n,m,d;
    cin>>n>>m>>d;
    cout<<fixed<<setprecision(10)<<((d==0)?1.:2.)*(n-d)/n*(m-1)/n;
}
