#include<algorithm>
#include<complex>
#include<ctype.h>
#include<iomanip>
#include<iostream>
#include<fstream>
#include<map>
#include<math.h>
#include<numeric>
#include<queue>
#include<set>
#include<stack>
#include<stdio.h>
#include<string>
#include<string>
#include<vector>

using namespace std;
typedef long long ll;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    double C;
    cin >> C;

    double r_in, r_out;
    cin >> r_in >> r_out;

    double r = (r_out - r_in) / 2;
    double S = r * r * M_PI;

    // 回転距離 l
    double diameter = 2 * (r_in + r);
    double l = diameter * M_PI;

    double V = S * l;
    double calorie = V * C;

    cout << setprecision(15);
    p(calorie);
    
    return 0;
}