fn input_num() -> usize {
    let mut line: String = String::new();
    std::io::stdin().read_line(&mut line).unwrap();
    line.trim().parse().unwrap()
}

fn input_chars() -> Vec<char> {
    let mut line: String = String::new();
    std::io::stdin().read_line(&mut line).unwrap();
    line.trim().chars().collect()
}

fn input_nums() -> (usize, f64, f64) {
    let mut line: String = String::new();
    std::io::stdin().read_line(&mut line).unwrap();
    let mut iter = line.split_whitespace();
    (
        iter.next().unwrap().parse().unwrap(),
        iter.next().unwrap().parse().unwrap(),
        iter.next().unwrap().parse().unwrap()
    )
}

fn input_vec_nums() -> Vec<usize> {
    let mut line: String = String::new();
    std::io::stdin().read_line(&mut line).unwrap();
    line.split_whitespace()
        .map(|x| x.parse().unwrap())
        .collect()
}

fn main() {
    let (mut l, s, d) = input_nums();
    let mut t = d / s;
    let mut ans = 0.0;
    while t > 0.0 {
        if t >= 1.0 {
            t -= 1.0;
            l += 1;
            if l % 24 <= 6 || l % 24 >= 19 {
                ans += 1.0;
            }
        } else {
            l += 1;
            if l % 24 <= 6 || l % 24 >= 18 {
                ans += t;
            }
            t = 0.0;
        }
    }
    println!("{}", ans);
}