#include<iostream>
#include<string>
using namespace std;
int main()
{float a,b,c;cin>>a>>b>>c;long i,j,u,z=0;string s;s+='.';
if(a!=c)cout<<"0"<<endl;else {
i=int(a);j=int(b);a-=i;b-=j;j+=i;b+=a;c=0;
z+=i*j;c+=a*b;u=int(i*b);c+=i*b-u;z+=u;u=int(a*j);
c+=a*j-u;z+=u;z*=2;c*=2;u=int(c);z+=u;c-=u;
cout<<z;c+=0.00001;if(c==0)cout<<".0000"<<endl;
else {for(i=0;i<4;i++){c*=10;s+=char(c+48);c-=int(c);}
cout<<s<<endl;}}}
