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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 start = Instant::now();
let mut low = 1 << (zeros + 1);
let p = loop {
println!("searching {}--{}", low, low * 2);
let sieve = primal::Sieve::new(low * 2);
match sieve.primes_from(low).find(|p| (p / 2).trailing_zeros() >= zeros) {
Some(p) => break p,
None => {}
}
low *= 2;
};
let time = start.elapsed();
println!("{} is the first prime with {} zeros, in {:?}",
p, zeros, time);
}
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