#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
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;
template<typename T>inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<typename T>inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}
//end

double R,H,D,a;
double inte(double x){
   double res;
   res=16*a*a*a*x*x*x*acos(D/2./a/x);
   res-=2*a*D*x*(a*x*sqrt(4-D*D/a/a/x/x)+3*sqrt(4*a*a*x*x-D*D));
   res-=D*D*D*log(x*(sqrt(4-D*D/a/a/x/x)+2));
   res+=3*D*D*D*log(a*(sqrt(4*a*a*x*x-D*D)+2*a*x));
   return res/a/24.;
}

int main(){
   cin>>R>>H>>D;
   double res=0; a=R/H;
   res=inte(H)-inte(D/a/2.);
   printf("%.12f\n",res);
   return 0;
}