只要超過 w+l 的話代表兩邊繩子繞過去會重覆到
所以把兩邊多出來的繩子做一個三角形，算出面積再加上兩個扇形的面積即可
//
// GGGGGGGGGGGGG CCCCCCCCCCCCC AAA
// GGG::::::::::::G CCC::::::::::::C A:::A
// GG:::::::::::::::G CC:::::::::::::::C A:::::A
// G:::::GGGGGGGG::::G C:::::CCCCCCCC::::C A:::::::A
// G:::::G GGGGGG C:::::C CCCCCC A:::::::::A
//G:::::G C:::::C A:::::A:::::A
//G:::::G C:::::C A:::::A A:::::A
//G:::::G GGGGGGGGGGC:::::C A:::::A A:::::A
//G:::::G G::::::::GC:::::C A:::::A A:::::A
//G:::::G GGGGG::::GC:::::C A:::::AAAAAAAAA:::::A
//G:::::G G::::GC:::::C A:::::::::::::::::::::A
// G:::::G G::::G C:::::C CCCCCC A:::::AAAAAAAAAAAAA:::::A
// G:::::GGGGGGGG::::G C:::::CCCCCCCC::::C A:::::A A:::::A
// GG:::::::::::::::G CC:::::::::::::::C A:::::A A:::::A
// GGG::::::GGG:::G CCC::::::::::::C A:::::A A:::::A
// GGGGGG GGGG CCCCCCCCCCCCCAAAAAAA AAAAAAA
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <climits>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <cctype>
#include <utility>
#include <ctime>
using namespace std;
#ifdef DEBUG
#define VAR(a,b) decltype(b) a=(b)
#define debug(...) printf("DEBUG: "),printf(\_\_VA\_ARGS\_\_)
#define gettime() end\_time=clock();printf("now running time is %.7f\\n",(float)(end\_time - start\_time)/CLOCKS\_PER\_SEC);
#else
#define VAR(a,b) \_\_typeof(b) a=(b)
#define debug(...)
#define gettime()
#endif
typedef unsigned int uint;
typedef long long int Int;
typedef unsigned long long int UInt;
#define Set(a,s) memset(a,s,sizeof(a))
#define Write(w) freopen(w,"w",stdout)
#define Read(r) freopen(r,"r",stdin)
#define Pln() printf("\\n")
#define I\_de(x,n)for(int i=0;i<n;i++)printf("%d ",x\[i\]);Pln()
#define De(x)printf(#x"%d\\n",x)
#define For(i,x)for(int i=0;i<x;i++)
#define CON(x,y) x##y
#define Pmz(dp,nx,ny)for(int hty=0;hty<ny;hty++){for(int htx=0;htx<nx;htx++){\\
printf("%d ",dp\[htx\]\[hty\]);}Pln();}
#define M 30005
#define PII pair<int,int\>
#define PB push\_back
#define oo INT\_MAX
#define Set\_oo 0x3f
#define FOR(a,b) for(VAR(a,(b).begin());a!=(b).end();++a)
#define eps 1e-9
#define X first
#define Y second
clock\_t start\_time=clock(), end\_time;
bool xdy(double x,double y){return x>y+eps;}
bool xddy(double x,double y){return x>y-eps;}
bool xcy(double x,double y){return x<y-eps;}
bool xcdy(double x,double y){return x<y+eps;}
int min3(int x,int y,int z){
int tmp=min(x,y);
return min(tmp,z);
}
int max3(int x,int y,int z){
int tmp=max(x,y);
return max(tmp,z);
}
double w,l,r;
double pi=2\*acos(0);
double solve(){
double r1=r-w;
double r2=r-l;
if(xcdy(w,0))return pi\*r\*r;
if(xcy(r,w+l)){
double ans=r\*r\*pi\*0.75;
if(xdy(r1,0))ans+=r1\*r1\*pi\*0.25;
if(xdy(r2,0))ans+=r2\*r2\*pi\*0.25;
return ans;
}
double d=sqrt(w\*w+l\*l);
double ang=acos((r1\*r1+d\*d-r2\*r2)/(2\*r1\*d));
double ang2=acos(w/d);
double a=pi-ang-ang2;
double ang3=acos((r2\*r2+d\*d-r1\*r1)/(2\*r2\*d));
double ang4=pi/2.-ang2;
double c=pi-ang-ang3;
double b=pi-ang3-ang4;
double ans=r\*r\*pi\*0.75;
ans+=r1\*r2\*sin(c)/2.;
ans-=w\*l/2.;
ans+=r1\*r1\*pi\*a/(2\*pi);
ans+=r2\*r2\*pi\*b/(2\*pi);
return ans;
}
int main() {
ios\_base::sync\_with\_stdio(0);
while(~scanf("%lf%lf%lf",&l,&w,&r)){
if(w>l)swap(w,l);
printf("%.10f\\n",solve());
}
}