#define _USE_MATH_DEFINES #include using namespace std; //template #define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++) #define ALL(v) (v).begin(),(v).end() typedef long long int ll; const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; const double eps=1e-12; templateinline bool chmax(T& a,T b){if(ainline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;} //end long double R,H,D,a; long double inte(long double x){ long double res; res=16*a*a*a*x*x*x*acos(D/2./a/x); res+=3*D*D*D*log(a*(sqrt(max((long double).0,4*a*a*x*x-D*D))+2*a*x)); res-=2*a*D*x*(a*x*sqrt(max((long double).0,4-D*D/a/a/x/x))+3*sqrt(max((long double).0,4*a*a*x*x-D*D))); res-=D*D*D*log(x*(sqrt(max((long double).0,4-D*D/a/a/x/x))+2)); return res/a/24.; } int main(){ cin>>R>>H>>D; long double res=0; a=R/H; res=inte(H)-inte(D*H/R/2.); printf("%.12Lf\n",res); return 0; }