#include <bits/stdc++.h>
#define PI 3.14159265359
using namespace std;
const int64_t MOD = 1e9 + 7;

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

	double ans;
	ans = PI * PI;
	ans *= Rout - Rin;
	ans *= Rout - Rin;
	ans /= 4;
	ans *= Rout + Rin;
	ans *= C;
	cout << ans << endl;
}