fn main() {
    let mut sc = Scanner::new();
    let a : f64 = sc.input();

    println!("{}", (15. + 5. * 5.0f64.sqrt()) / 12. * a * a * a);
}


struct Scanner { s : std::collections::VecDeque<String> } #[allow(unused)] impl Scanner { fn new() -> Self { use std::io::Read; let mut s = String::new(); std::io::stdin().read_to_string(&mut s).unwrap(); Self { s : s.split_whitespace().map(|s| s.to_string()).collect() } } fn reload(&mut self) -> () { use std::io::Read; let mut s = String::new(); std::io::stdin().read_to_string(&mut s).unwrap(); self.s = s.split_whitespace().map(|s| s.to_string()).collect(); } fn usize(&mut self) -> usize { self.input() } fn usize1(&mut self) -> usize { self.input::<usize>() - 1 } fn isize(&mut self) -> isize { self.input() } fn i32(&mut self) -> i32 { self.input() } fn i64(&mut self) -> i64 { self.input() } fn i128(&mut self) -> i128 { self.input() } fn u8(&mut self) -> u8 { self.input() } fn u32(&mut self) -> u32 { self.input() } fn u64(&mut self) -> u64 { self.input() } fn u128(&mut self) -> u128 { self.input() } fn edge(&mut self) -> (usize, usize) { (self.usize1(), self.usize1()) } fn edges(&mut self, m : usize) -> Vec<(usize, usize)> { let mut e = Vec::with_capacity(m); for _ in 0..m { e.push(self.edge()); } e } fn wedge<T:std::str::FromStr>(&mut self) -> (usize, usize, T) { (self.usize1(), self.usize1(), self.input()) } fn wedges<T:std::str::FromStr>(&mut self, m : usize) -> Vec<(usize, usize, T)> { let mut e = Vec::with_capacity(m); for _ in 0..m { e.push(self.wedge()); } e } fn input<T>(&mut self) -> T where T: std::str::FromStr { if self.s.is_empty() { self.reload(); } if let Some(head) = self.s.pop_front() { head.parse::<T>().ok().unwrap() } else { panic!() } } fn tuple<T, U>(&mut self) -> (T, U) where T: std::str::FromStr, U: std::str::FromStr { (self.input(), self.input()) } fn vec<T>(&mut self, n: usize) -> Vec<T> where T: std::str::FromStr { if self.s.is_empty() { self.reload(); } self.s.drain(..n).map(|s| s.parse::<T>().ok().unwrap() ).collect::<Vec<T>>() } fn nvec<T>(&mut self) -> Vec<T> where T: std::str::FromStr { let n : usize = self.input(); self.vec(n) } fn chars(&mut self) -> Vec<char> { let s : String = self.input(); s.chars().collect() } fn bytes(&mut self) -> Vec<u8> { let s : String = self.input(); s.bytes().collect() } }