fn main() {
    proconio::input! {
        l: u64,
    }
    let ans = (1..=l).sum::<u64>();
    println!("{ans}");
}

fn proc(a: u64, b: u64) -> u64 {
    b.div_ceil(a)
}

#[cfg(test)]
mod test {
    use super::*;
    #[test]
    fn test() {
        assert_eq!(proc(2, 5), 3);
    }
}