#include<bits/stdc++.h>
const double PIE=3.1415926535;
using namespace std;
int main(){
    double C,Rin,Rout;
    cin>>C>>Rin>>Rout;
    double dif=(Rout-Rin)/2;
    double ans=dif*dif*PIE*(Rin+dif)*2*PIE*C;
    printf("%.8lf\n",ans);
    return 0;
}