#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define popcount __builtin_popcount using namespace std; typedef long long ll; typedef pair P; int main() { double r, h, d; cin>>r>>h>>d; double ans=0; const int loop=10000000; double h1=h/loop; for(double i=h1/2; i<=h; i+=h1){ double r1=r*i/h; if(d>=2*r1) continue; double t=acos(d/(2*r1))*2; ans+=h1*r1*r1*(t-sin(t)); } printf("%.7lf\n", ans); return 0; }