// Copyright (C) 2015 by Alexandru Cojocaru

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

use std::collections::BitSet;
use std::f64;
// use std::iter::range_step;

fn to_index(n: u64) -> usize {
	((n-3)/2) as usize
}

fn from_index(i: usize) -> u64 {
	(i*2 + 3) as u64
}

fn primes(n: u64) -> Vec<u64> {
	let mut p = BitVec::from_elem(to_index(n) + 1, false);
	for i in (3..f64::sqrt(n as f64) as u64 + 1).step_by(2) {
	    for j in (i*i..n+1).step_by(i*2) {
			p.set(to_index(j), true);
		}
	}
    
	let mut v = Vec::<u64>::new();
	v.push(2);
	for i in 0..p.len() {
		if p[i] == false {
			v.push(from_index(i))
		}
	}
	v
}

fn main() {
	println!("{}", primes(15485863).len());
}