struct Num { rdigits: Vec<u8> }

impl Num {
    pub fn from(s: &String) -> Num {
        let rd: Vec<u8> = s.chars().rev()
                    .map(|c| String::from(c).parse::<u8>().unwrap())
                    .collect();
        Num { rdigits: rd }
    }
    pub fn add(&self, n: &Num) -> Num {
        let mut xs = self.rdigits.clone();
        let mut ys = n.rdigits.clone();
        let mut rs: Vec<u8> = Vec::new();

        while xs.len() < ys.len() { xs.push(0); }
        while ys.len() < xs.len() { ys.push(0); }

        let mut rm = 0u8;
        for (a, b) in xs.iter().zip(ys.iter()) {
            if a + b + rm > 9 {
                rs.push((a + b + rm) - 10);
                rm = 1u8;
            } else {
                rs.push(a + b + rm);
                rm = 0u8;
            }
        }
        if rm > 0 { rs.push(1u8); }

        Num { rdigits: rs }
    }
    pub fn len(&self) -> usize { self.rdigits.len() }
    pub fn print(&self) {
        for c in self.rdigits.iter().rev() { print!("{}", c); };
        println!("");
    }
}


fn main() {
    let mut fa = Num::from(&String::from("1"));
    let mut fb = Num::from(&String::from("1"));
    let mut i = 2;
    let l = 1000usize;

    while fb.len() < l {
        let fc = fa.add(&fb);
        fa = fb;
        fb = fc;
        i += 1;
    }
    fb.print();
    println!("-----------");
    println!("[{}]", i);

}