#include <algorithm>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
using namespace std;
typedef pair<int, int> pii;
typedef vector<int> vi;
#define rep(i,x) for(int i=0;i<(int)(x);i++)

int main(){
	int c;
	double rin, rout;
	cin >> c >> rin >> rout;
	double ans = ((rout-rin)/2)*((rout-rin)/2)*M_PI*(rout+rin)*M_PI*c;
	printf("%.10f\n", ans);
	return 0;
}