#include<bits/stdc++.h>
using namespace std;
int main(){
    int c,rin,rout;
    cin>>c>>rin>>rout;
    double pi,r,ans;
    pi=4.0*atan(1.0);
    r=(rout-rin)/2.0;
    ans=2*pi*pi*r*r*(rin+r)*c;
    cout<<fixed<<setprecision(10)<<ans<<endl;
}