use std::io::*; use std::str::FromStr; /* const LOW_CASE_ALPHABET: [char; 26] = [ 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', ]; */ fn main() { let n: usize = read(); let tmp = (n + 1) / 2; print!("{}",tmp * (tmp + 1) / 2); } pub fn perfect(value_1: usize) -> usize { let mut perfect_number = Vec::new(); for _i in 2..=value_1 { let mut tmp = 0; for _j in 1..=((_i as f64).powf(0.5)) as usize { if _i % _j == 0 { if _j * _j == _i { tmp += _j; } else { tmp += _j + (_i / _j); } } } tmp -= _i; if tmp == _i { perfect_number.push(_i); } } for _i in 0..perfect_number.len() - 1 { println!("{}", perfect_number[_i]); } return perfect_number[perfect_number.len() - 1]; } pub fn prime_number(value_1: usize, value_2: usize) -> usize { let mut primary = Vec::new(); let mut tmp = 0; primary.push(2); for _i in 2..=value_1 { let mut flag = 0; for _j in 0..primary.len() { if _i % primary[_j] == 0 { flag = 1; break; } } if flag == 0 { primary.push(_i); } if primary.len() == value_2 { tmp = 1; return primary[primary.len() - 1]; } } return 0; } pub fn ctoi(c: char) -> isize { let n = c as isize - '0' as isize; return n; } pub fn stoi(c: String) -> isize { let n = c.parse::().unwrap(); return n; } pub fn find_char(sentence: Vec, target: char, start: isize) -> isize { for _i in start as usize..sentence.len() { if sentence[_i] == target { return _i as isize; } } return -1; } pub fn hex_to_binary_2(hex_string: String, x: u32) -> Option { match i64::from_str_radix(&hex_string, x) { Ok(decimal) => Some(format!("{}", decimal)), Err(_) => None, } } pub fn hex_to_binary(hex_string: &str, x: u32) -> Option { match i64::from_str_radix(hex_string, x) { Ok(decimal) => Some(format!("{}", decimal)), Err(_) => None, } } pub fn my_floor(x: f64) -> f64 { let rounded = (x * 1000.0).floor() / 1000.0; rounded } pub fn upper_lower(x: char) -> char { let result: char; if x.is_uppercase() { result = x.to_ascii_lowercase(); } else if x.is_lowercase() { result = x.to_ascii_uppercase(); } else { result = x; } result } pub fn maxf_2(x: f64, y: f64) -> f64 { let result; if x >= y { result = x; } else { result = y; } result } pub fn max_2(x: isize, y: isize) -> isize { let result; if x >= y { result = x; } else { result = y; } result } pub fn max_u_2(x: usize, y: usize) -> usize { let result; if x >= y { result = x; } else { result = y; } result } pub fn min_u_2(x: usize, y: usize) -> usize { let result; if x <= y { result = x; } else { result = y; } result } pub fn min_2(x: isize, y: isize) -> isize { let result; if x >= y { result = y; } else { result = x; } result } pub fn min_2_i32(x: i32, y: i32) -> i32 { let result; if x >= y { result = y; } else { result = x; } result } pub fn max_3(x: isize, y: isize, z: isize) -> isize { let result; if x >= y && y >= z { result = x; } else if x >= z && z >= y { result = x; } else if y >= x && x >= z { result = y; } else if y >= z && z >= x { result = y; } else if z >= x && x >= y { result = z; } else { result = z; } result } pub fn max_u_3(x: usize, y: usize, z: usize) -> usize { let result; if x >= y && y >= z { result = x; } else if x >= z && z >= y { result = x; } else if y >= x && x >= z { result = y; } else if y >= z && z >= x { result = y; } else if z >= x && x >= y { result = z; } else { result = z; } result } pub fn min_3(x: isize, y: isize, z: isize) -> isize { let result; if x <= y && y <= z { result = x; } else if x <= z && z <= y { result = x; } else if y <= x && x <= z { result = y; } else if y <= z && z <= x { result = y; } else if z <= x && x <= y { result = z; } else { result = z; } result } pub fn min_u_3(x: usize, y: usize, z: usize) -> usize { let result; if x <= y && y <= z { result = x; } else if x <= z && z <= y { result = x; } else if y <= x && x <= z { result = y; } else if y <= z && z <= x { result = y; } else if z <= x && x <= y { result = z; } else { result = z; } result } pub fn read_text() -> String { let mut word = String::new(); std::io::stdin().read_line(&mut word).ok(); let answer = word.trim().to_string(); answer } pub fn read_array() -> Vec { let array: String = read(); let chars: Vec = array.trim().chars().collect::>(); chars } pub fn read() -> T { let stdin = stdin(); let stdin = stdin.lock(); let token: String = stdin .bytes() .map(|c| c.expect("failed to read char") as char) .skip_while(|c| c.is_whitespace()) .take_while(|c| !c.is_whitespace()) .collect(); token.parse().ok().expect("failed to parse token") }