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);
}