#include "bits/stdc++.h"

#define REP(i, n) for(decltype(n) i = 0; i < (n); i++)
#define REP2(i, x, n) for(decltype(x) i = (x); i < (n); i++)
#define RREP(i, n) for (decltype(n) i = (n) - 1;i >= 0; i--)

#define ALL(a) (a).begin(),(a).end()
#define SORT(c) sort((c).begin(),(c).end())
#define DESCSORT(c) sort(c.begin(), c.end(), greater<int>())

#define LL long long int
#define LD long double

#define PI 3.14159265358979

#define _CRT_SECURE_NO_WARNINGS

using namespace std;

//================================================

int main() {
	double C, Rin, Rout;
	cin >> C >> Rin >> Rout;

	double ans = ((Rout - Rin) / 2) * ((Rout - Rin) / 2) * PI * 2 * PI * ((Rin + Rout) / 2) * C;
	printf("%.14f\n", ans);
	return 0;
}