use std::io::Read;

fn main() {
    let mut input = String::new();
    std::io::stdin().read_to_string(&mut input).unwrap();
    let mut input = input.split_whitespace();
    let t: usize = input.next().unwrap().parse().unwrap();
    let s: usize = input.next().unwrap().parse().unwrap();
    let d: usize = input.next().unwrap().parse().unwrap();
    let mut ans = 0.0f64;
    let mut remain = d;
    let mut now = t;
    while s <= remain {
        if 18 <= now || now < 6 {
            ans += 1.0;
        }
        remain -= s;
        now += 1;
        if now == 24 {
            now = 0;
        }
    }
    if 18 <= now || now < 6 {
        ans += remain as f64 / s as f64;
    }
    println!("{:.15}", ans);
}