#include <bits/stdc++.h>
//#include <chrono>
//#pragma GCC optimize("O3")
using namespace std;
#define reps(i,s,n) for(int i = s; i < n; i++)
#define rep(i,n) reps(i,0,n)
#define Rreps(i,n,e) for(int i = n - 1; i >= e; --i)
#define Rrep(i,n) Rreps(i,n,0)
#define ALL(a) a.begin(), a.end()

using ll = long long;
using vec = vector<ll>;
using mat = vector<vec>;

ll N,M,H,W,Q,K,A,B;
string S;
using P = pair<ll, ll>;
const ll INF = (1LL<<60);

template<class T> bool chmin(T &a, const T &b){
    if(a > b) {a = b; return true;}
    else return false;
}
template<class T> bool chmax(T &a, const T &b){
    if(a < b) {a = b; return true;}
    else return false;
}
template<class T> void my_printv(std::vector<T> v,bool endline = true){
    if(!v.empty()){
        for(std::size_t i{}; i<v.size()-1; ++i) std::cout<<v[i]<<" ";
        std::cout<<v.back();
    }
    if(endline) std::cout<<std::endl;
}

long double r, h, d;
vector<long double> memo;
void calc(long double lb, long double ub){
    long double z = (ub + lb) / 2;
    if(ub - lb < 1e-6){
        memo.push_back((lb * lb * log(sqrt(1 - lb * lb) + 1) + ub * ub * log(sqrt(1 - ub * ub) + 1)) * (ub - lb) * 0.5);
    }else{
        calc(lb, z); calc(z, ub);
    }
}
int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    ll R, D;
    cin>>r>>h>>d;
    R = (ll)(r * 100 + 0.5);
    H = (ll)(h * 100 + 0.5);
    D = (ll)(d * 100 + 0.5);
    if(false){//D == 0 || D == R){
        cout<<(D == 0 ? acos((long double)-1.0) * r * r * h / 3.0 : 0)<<endl;
    }else{
        long double b = (long double)D / (R * 2), sq = sqrt(- b * b + 1.0);
        /*
        calc(lb, 1);
        sort(ALL(memo));
        cout<<fixed<<setprecision(10)<<(- accumulate(ALL(memo), (long double)0.0) * 2.0 + acos(lb) - lb * sqrt(- lb * lb + 1.0)
        + (lb*lb*lb * (1.0 - log(lb) * 3.0) - 1.0) * 2.0 / 9) * R * R * H * (long double)1e-6<<endl;
         */
        cout<<fixed<<setprecision(10)<<(acos(b) - b * sq * 2.0 + b * b * b * log((sq + 1.0) / b)) * r * r * h * 2.0 / 3.0<<endl;
    }
}