#include <bits/stdc++.h>
#define INF 114514810
#define PI 3.14159265358979
#define FOR(i, r, n) for(int i=(r); i<(n); i++) 
#define REP(i, n) FOR(i, (0), n)

using namespace std;

double ans;
int c, r1, r2;

int main(){
	cin >> c >> r1 >> r2;
	ans = PI*(r1 + r2)*PI*(r2 - r1)*(r2 - r1) / 4.00000000*c;
	cout.precision(15);
	cout << ans << endl;
}