#include <bits/stdc++.h>

typedef long long ll;
#define rep(i, b) for(int i = 0; i < b; i++)
#define repi(i, a, b) for(int i = a; i < b; i++)
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) __typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define MAX_V 1001
#define MAX_E 401
#define MOD 1000000007
#define EPS 1e-5
#define INF INT_MAX
#define PI 3.14159265358979323846264338327950288
inline ll toll(std::string s) { ll v; std::istringstream sin(s); sin >> v; return v; }
template<class T> inline std::string toString(T x) { std::ostringstream sout; sout << x; return sout.str(); }
using namespace std;
typedef pair<int, int> pii;

int main()
{
	double C, Rin, Rout;
	cin >> C >> Rin >> Rout;
	cout << fixed << setprecision(6) << C * 2 * PI * (Rout - ((Rout - Rin) / 2)) * PI * ((Rout - Rin) / 2) * ((Rout - Rin) / 2) << endl;
	return 0;
}