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); } // 1 -> [1] k // 2 -> [2] kk, kp // 3 -> [2] kkp, kpk // 3 -> "2" + 0 // 4 -> [3] kkpk, kpkp, kpkk // 4 -> "3" + 1, "2" + 1 // 5 -> [4] kkpkk, kkpkp, kpkkp, kpkpk // 5 -> "4" + 1, "3" + 2, "2" + 2 // 6 -> [5] kkpkkp, kkpkpk, kpkkpk, kpkpkk, kpkpkp // 6 -> "5" + 1, "4" + 2, "3" + 3, "2" + 3 // 7 -> [7] kkpkkpk, kkpkpkk, kkpkpkpk, kpkkpkk, kpkkpkp, kpkpkkp, kpkpkpk // 7 -> "6" + 2, "5" + 3, "4" + 4, "3" + 5, "2" + 5 // 8 -> [9] kkpkkpkk, kkpkkpkp, kkpkpkkpk, kkpkpkpk, kpkkpkkp, kpkkpkpk, kpkpkkpk, kpkpkpkk, kpkpkpkp // q(n) = q(n-3) + q(n-2) fn process(mut reader: R, mut writer: W) -> () where R: BufRead, W: Write { input! { stdin = reader, n: usize } static HASH: usize = 1000000007; let mut memo: Vec = vec![0; n + 1]; memo[1] = 1; memo[2] = 2; memo[3] = 2; for i in 4..n + 1 { memo[i] = (memo[i - 3] + memo[i - 2]) % HASH; } write!(writer, "{}", memo[n]); } #[cfg(test)] mod tests { use super::*; #[test] fn sample1() { assert_judge!(process, "3", "2"); } #[test] fn sample2() { assert_judge!(process, "4", "3"); } #[test] fn sample3() { assert_judge!(process, "100", "831891005"); } }