#include<bits/stdc++.h>
using namespace std;

int main(){
    int c,rin,rout;
    double ans,r;
    cin >> c >> rin >> rout;

    r=(double)(rout-rin)/2;
    ans=r*r*M_PI;
    ans*=(r+rin)*2*M_PI;
    printf("%.6f\n",ans*c);

    return 0;
}