#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>
#include <functional>
#include <limits>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <complex>

using namespace std;

#define INF (INT_MAX/3)
#define PI (2*acos(0.0))
#define EPS (1e-8)

typedef long long ll;
typedef unsigned long long ull;

int main(){
    ios_base::sync_with_stdio(0);
    int C, Rin, Rout;
    double r, l, S, V;
    cin >> C >> Rin >> Rout;
    r = 1.0 * (Rout - Rin) / 2;
    S = PI * r * r;
    l = 2 * PI * (Rin + r);
    V = S * l;
    printf("%.10f\n", V * C);
    return 0;
}