#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        #[cfg(feature = "single_testcase")]
        {
            eprint!("[line:{}] ", line!());
            eprintln!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
        }
    }
}

fn get_time() -> f64 {
    static mut STIME: f64 = -1.0;
    let t = std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .unwrap();
    let ms = t.as_secs() as f64 + t.subsec_nanos() as f64 * 1e-9;
    unsafe {
        if STIME < 0.0 {
            STIME = ms;
        }
        ms - STIME
    }
}

//--------------------------------------------------------------------------------
// https://atcoder.jp/contests/intro-heuristics/submissions/14832097
// let D = read!(usize);
// let c = read!([i64]);
// let s = read!([i64]; D);

#[allow(dead_code)]
fn readln() -> String {
    let mut line = String::new();
    ::std::io::stdin()
        .read_line(&mut line)
        .unwrap_or_else(|e| panic!("{}", e));
    line
}

#[allow(unused_macros)]
macro_rules! read {
	($($t:tt),*; $n:expr) => {{
		let stdin = ::std::io::stdin();
		let ret = ::std::io::BufRead::lines(stdin.lock()).take($n).map(|line| {
			let line = line.unwrap();
			let mut it = line.split_whitespace();
			_read!(it; $($t),*)
		}).collect::<Vec<_>>();
		ret
	}};
	($($t:tt),*) => {{
		let line = readln();
		let mut it = line.split_whitespace();
		_read!(it; $($t),*)
	}};
}

macro_rules! _read {
	($it:ident; [char]) => {
		_read!($it; String).chars().collect::<Vec<_>>()
	};
	($it:ident; [u8]) => {
		Vec::from(_read!($it; String).into_bytes())
	};
	($it:ident; usize1) => {
		$it.next().unwrap_or_else(|| panic!("input mismatch")).parse::<usize>().unwrap_or_else(|e| panic!("{}", e)) - 1
	};
	($it:ident; [usize1]) => {
		$it.map(|s| s.parse::<usize>().unwrap_or_else(|e| panic!("{}", e)) - 1).collect::<Vec<_>>()
	};
	($it:ident; [$t:ty]) => {
		$it.map(|s| s.parse::<$t>().unwrap_or_else(|e| panic!("{}", e))).collect::<Vec<_>>()
	};
	($it:ident; $t:ty) => {
		$it.next().unwrap_or_else(|| panic!("input mismatch")).parse::<$t>().unwrap_or_else(|e| panic!("{}", e))
	};
	($it:ident; $($t:tt),+) => {
		($(_read!($it; $t)),*)
	};
}

//--------------------------------------------------------------------------------
// https://atcoder.jp/contests/hokudai-hitachi2017-1/submissions/1797182
// u32 -> usize

pub struct XorShift {
    pub x: [usize; 4],
}

impl XorShift {
    pub fn new(mut seed: usize) -> XorShift {
        let mut x = [0; 4];
        for i in 0..4 {
            seed = 1812433253usize
                .wrapping_mul(seed ^ (seed >> 30))
                .wrapping_add(i as usize);
            x[i] = seed;
        }
        XorShift { x: x }
    }
    pub fn next_usize(&mut self) -> usize {
        let t = self.x[0] ^ (self.x[0] << 11);
        for i in 0..3 {
            self.x[i] = self.x[i + 1]
        }
        self.x[3] = self.x[3] ^ (self.x[3] >> 19) ^ t ^ (t >> 8);
        self.x[3]
    }
    /// [0, n)
    pub fn next(&mut self, n: usize) -> usize {
        loop {
            let t = self.next_usize();
            let r = t % n;
            if (t - r).checked_add(n).is_some() {
                return r;
            }
        }
    }
    pub fn shuffle<T>(&mut self, a: &mut [T]) {
        for i in 0..a.len() {
            let j = i + self.next((a.len() - i)) as usize;
            a.swap(i, j);
        }
    }
}

//--------------------------------------------------------------------------------

const SEED: u32 = 890482;
const TIME_LIMIT: f64 = 0.98;

fn main() {
    get_time();

    let n = read!(i32);
    let mut sm = 0;
    for i in 1..=n {
        sm += i;
    }

    println!("{}", sm);

    eprintln!("time_elapsed: {:.3}", get_time());
}