fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let mut d = "1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991".chars().map(|c| c as usize - '0' as usize).collect::<Vec<_>>();
    let length = d.len();

    d.reverse();
    let mut result = vec![];
    let mut carry = 0usize;
    for i in 0..length {
        carry += d[i] * n;
        result.push(carry % 10);
        carry /= 10;
    }
    println!("{}.{}", carry, result.iter().rev().map(|v| v.to_string()).collect::<Vec<_>>().join(""));
}