#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
using namespace std;
typedef long long LL;
typedef vector<int> VI;

int main() {
	int c, ri, ro;
	cin >> c >> ri >> ro;
	double r = (ro - ri) / 2.0;
	double ans = (ro + ri) * M_PI * r * r * M_PI;
	cout << setprecision(10) << fixed << ans * c << endl;
	return 0;
}