P9693.rs

/*
    Author : quickn (quickn.ga)
    Email  : quickwshell@gmail.com
*/

use std::io::{self, BufWriter, Write};
use std::str;

/* https://github.com/EbTech/rust-algorithms */

/// Same API as Scanner but nearly twice as fast, using horribly unsafe dark arts
/// **REQUIRES** Rust 1.34 or higher
pub struct UnsafeScanner<R> {
    reader: R,
    buf_str: Vec<u8>,
    buf_iter: str::SplitAsciiWhitespace<'static>,
}

impl<R: io::BufRead> UnsafeScanner<R> {
    pub fn new(reader: R) -> Self {
        Self {
            reader,
            buf_str: Vec::new(),
            buf_iter: "".split_ascii_whitespace(),
        }
    }

    /// This function should be marked unsafe, but noone has time for that in a
    /// programming contest. Use at your own risk!
    pub fn token<T: str::FromStr>(&mut self) -> T {
        loop {
            if let Some(token) = self.buf_iter.next() {
                return token.parse().ok().expect("Failed parse");
            }
            self.buf_str.clear();
            self.reader
                .read_until(b'\n', &mut self.buf_str)
                .expect("Failed read");
            self.buf_iter = unsafe {
                let slice = str::from_utf8_unchecked(&self.buf_str);
                std::mem::transmute(slice.split_ascii_whitespace())
            }
        }
    }
}

use std::cmp::min;

fn main() {
    let (stdin, stdout) = (io::stdin(), io::stdout());
    let (mut scan, mut sout) = (
        UnsafeScanner::new(stdin.lock()),
        BufWriter::new(stdout.lock()),
    );
    let mut n: usize = scan.token();
    let mut t = 1;
    while n != 0 {
        let (mut power_2, mut power_5): (usize, usize) = (0, 0);
        // 2
        let mut r = 2;
        while r <= n {
            power_2 += n / r;
            r <<= 1;
        }
        // 5
        r = 5;
        while r <= n {
            power_5 += n / r;
            r *= 5;
        }
        writeln!(sout, "Case #{}: {}", t, min(power_2, power_5)).ok();
        t += 1;
        n = scan.token();
    }
}