#include<iostream>
#include<cstdio>
using namespace std;
int main(){
    const double pi=3.1415926;
    double a,b,c,ans=0;
    cin>>a>>b>>c;
    ans+=a*c;
    ans+=(a+c)*b;
    ans+=pi*c*c/4;
    ans/=10000;
    printf("%.3lf\n",ans);
    return 0;
}