use std::env;
use std::time::Instant;

fn main() {
    let mut args = env::args();
    let zeros = args
        .nth(1).and_then(|s| s.parse::<f64>().ok().map(|x| x as u32))
        .unwrap_or(10);

    let step = 1 << (zeros + 1);
    let start = Instant::now();
    let mut it = step + 1;
    while !primal::is_prime(it) {
        it += step;
    }
    let p = it;
    let time = start.elapsed();

    println!("{} is the first prime with {} zeros, in {:?}",
             p, zeros, time);
}