#![allow(unused_imports)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;
use std::ops::Bound::*;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn main() {
    let v = read_vec::<f64>();
    let (a, b, c) = (v[0], v[1], v[2]);
    let A = ((b * b + c * c - a * a) / 2.0 / b / c).acos();
    let B = ((a * a + c * c - b * b) / 2.0 / a / c).acos();
    let C = ((a * a + b * b - c * c) / 2.0 / a / b).acos();
    let all = 0.5 * a * b * C.sin();
    let aa = 0.5 * 0.5 * 0.5 * a * b * C.sin();
    let bb = 0.5 * 0.5 * 0.5 * a * c * B.sin();
    let cc = 0.5 * 0.5 * 0.5 * b * c * A.sin();
    let ans = all - aa - bb - cc;
    println!("{}", ans);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}