#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <map>
#include <cmath>
#include <queue>
#include <numeric>
#include <climits>
#include <iterator>
#include <iomanip>
#include <stack>
#include <set>
#include <cstdio>
#include <bitset>
#include <functional>
#include <tuple>
#include <list>
#include <deque>
#include <sstream>
using namespace std;
const constexpr int INF = 1e9;

#define FOR(i, a, n) for (ll i = (ll)a; i<(ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)

typedef long long ll;
typedef vector<int> VI;
typedef pair<ll, ll> P;
struct Less{
   bool operator()(const pair<string, int>&a, const pair<string, int>&b){
        if(a.first==b.first){
            return a.second < b.second;
        }
       return a.first < b.first;
    }
};
const constexpr ll MOD = 1e9 + 7;


ll extGCD(ll a, ll b, ll& x, ll& y){
    if(b==0){
        x=1;
        y=0;
        return a;
    }
    ll d = extGCD(b, a%b, y, x);
    y -= a/b*x;
    return d;
}
ll GCD(ll a, ll b){
    if(b==0) return a;
    return GCD(b, a%b);
}

int main() {
    double C, Rin, Rout; cin >> C >> Rin >> Rout;
    double r=(Rout-Rin)/2;
    double gx = Rin + r;
    cout << fixed << setprecision(10) << C*2*M_PI*gx*r*r*M_PI << endl;
        
    return 0;
}