#include <bits/stdc++.h>
using namespace std;
double a,b,c,d,e,f,g,h;
int main(){
    cin>>a>>b>>c;
    d=a+c;
    e=3.1415926535;
    f=c*c;
    g=1/4;
    h=10000;
    cout<<fixed<<setprecision(3)<<(a*c+d*b+e*f*g)/h;
    return 0;
}