use std::io; use std::io::{BufRead, Write}; macro_rules! input { (source = $s:expr, $($r:tt)*) => { let mut iter = $s.split_whitespace(); input_inner!{iter, $($r)*} }; (stdin = $s:expr, $($r:tt)*) => { let s = { let mut s = String::new(); $s.read_to_string(&mut s).unwrap(); s }; let mut iter = s.split_whitespace(); input_inner!{iter, $($r)*} }; } macro_rules! input_inner { ($iter:expr) => {}; ($iter:expr, ) => {}; ($iter:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($iter, $t); input_inner!{$iter $($r)*} }; } macro_rules! read_value { ($iter:expr, ( $($t:tt),* )) => { ( $(read_value!($iter, $t)),* ) }; ($iter:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($iter, $t)).collect::>() }; ($iter:expr, chars) => { read_value!($iter, String).chars().collect::>() }; ($iter:expr, usize1) => { read_value!($iter, usize) - 1 }; ($iter:expr, $t:ty) => { $iter.next().unwrap().parse::<$t>().expect("Parse error") }; } #[allow(unused_macros)] macro_rules! assert_judge { ($method:ident, $input:expr, $expected:expr) => { { let input = $input.as_bytes(); let mut output = Vec::new(); $method(&input[..], &mut output); let output = String::from_utf8(output).expect("Not UTF-8"); assert_eq!($expected, output); } }; } #[allow(unused_macros)] macro_rules! assert_judge_with_output { ($method:ident, $input:expr) => { { let input = $input.as_bytes(); let mut output = Vec::new(); $method(&input[..], &mut output); String::from_utf8(output).expect("Not UTF-8") } }; } fn main() { let stdio = io::stdin(); let input = stdio.lock(); let output = io::stdout(); process(input, output); } fn process(mut reader: R, mut writer: W) -> () where R: BufRead, W: Write { input! { stdin = reader, n: usize } let original_n = n; let n = if n % 2 == 0 { n / 2 } else { n }; let rt_n = (n as f64).sqrt(); let limit = rt_n.ceil() as usize; // let mut vec: Vec<_> = (3..limit + 1).collect(); // // for p in 3..limit + 1 { // vec.retain(|&x| x <= p || x % p != 0); // } // // for p in vec { // if n % p == 0 { // write!(writer, "{}", p); // return; // } // } // // write!(writer, "{}", original_n); let mut least_primes = vec![0; limit + 1]; least_primes[1] = 1; for i in 3..limit + 1 { if least_primes[i] == 0 { if n % i == 0 { write!(writer, "{}", i); return; } least_primes[i] = i; for j in (2 * i..limit + 1).step_by(i) { if least_primes[j] == 0 { least_primes[j] = i; } } } } write!(writer, "{}", original_n); } #[cfg(test)] mod tests { use super::*; #[test] fn sample1() { assert_judge!(process, "9", "3"); } #[test] fn sample2() { assert_judge!(process, "30", "3"); } #[test] fn sample3() { assert_judge!(process, "114514", "31"); } #[test] fn sample4() { assert_judge!(process, "8573912969", "421"); } }