// Original: https://github.com/tanakh/competitive-rs #[allow(unused_macros)] macro_rules! input { (source = $s:expr, $($r:tt)*) => { let mut iter = $s.split_whitespace(); let mut next = || { iter.next().unwrap() }; input_inner!{next, $($r)*} }; ($($r:tt)*) => { let stdin = std::io::stdin(); let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock())); let mut next = move || -> String{ bytes .by_ref() .map(|r|r.unwrap() as char) .skip_while(|c|c.is_whitespace()) .take_while(|c|!c.is_whitespace()) .collect() }; input_inner!{next, $($r)*} }; } #[allow(unused_macros)] macro_rules! input_inner { ($next:expr) => {}; ($next:expr, ) => {}; ($next:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($next, $t); input_inner!{$next $($r)*} }; ($next:expr, mut $var:ident : $t:tt $($r:tt)*) => { let mut $var = read_value!($next, $t); input_inner!{$next $($r)*} }; } #[allow(unused_macros)] macro_rules! read_value { ($next:expr, ( $($t:tt),* )) => { ( $(read_value!($next, $t)),* ) }; ($next:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($next, $t)).collect::>() }; ($next:expr, [ $t:tt ]) => { { let len = read_value!($next, usize); (0..len).map(|_| read_value!($next, $t)).collect::>() } }; ($next:expr, chars) => { read_value!($next, String).chars().collect::>() }; ($next:expr, bytes) => { read_value!($next, String).into_bytes() }; ($next:expr, usize1) => { read_value!($next, usize) - 1 }; ($next:expr, $t:ty) => { $next().parse::<$t>().expect("Parse error") }; } #[allow(dead_code)] fn chmin(x: &mut T, y: T) -> bool where T: PartialOrd + Copy, { *x > y && { *x = y; true } } #[allow(dead_code)] fn chmax(x: &mut T, y: T) -> bool where T: PartialOrd + Copy, { *x < y && { *x = y; true } } #[allow(unused_imports)] use std::cmp::{max, min}; #[allow(unused_imports)] use std::collections::{BTreeMap, BTreeSet, BinaryHeap, VecDeque}; fn main() { input! { n:usize } let sieve = eratosthenes_sieve(n); let mut primes = vec![]; for (i, &v) in sieve.iter().enumerate() { if v { primes.push(i); } } let mut cnt = 0; let lim = primes.len(); for i in 0..lim { let r2 = primes[i].pow(2) as i64; for j in 0..lim { let p = primes[j] as i64; let b = r2 - p; if b < 0 || n <= b as usize{ continue; } if sieve[b as usize] { cnt += 1; } } } println!("{}", cnt); } pub fn eratosthenes_sieve(n: usize) -> Vec { let n = n + 1; let mut res = vec![true; n]; res[0] = false; res[1] = false; for i in 2..n { if !res[i] { continue; } for j in 2..n { if i * j >= n { break; } // 素数の倍数は素数ではない res[i * j] = false; } } res }