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

#define REP(i, n) for(int i=0; i<(n); i++)

double C, R1, R2;
signed main()
{
    cin >> C >> R1 >> R2;
    double r = (R2 + R1)/2;
    double m = (R2 - R1)/2;
    double cal = M_PI * pow(m, 2) * 2 * M_PI * r * C;
    printf("%.14f\n", cal);
    return 0;
}