Rust template just taking input from stdin for competitive programming.

main.rs

use std::io::{self, Read};

macro_rules! input {
    ($it: expr) => ($it.next().unwrap().parse().unwrap());
    ($it: expr, $T: ty) => ($it.next().unwrap().parse::<$T>().unwrap());
}

fn main() {
    let mut buf = String::new();
    io::stdin().read_to_string(&mut buf).unwrap();

    let mut it = buf.split_whitespace();

    let n: usize = input!(it);
    let a: Vec<u64> = (0..n).map(|_| input!(it)).collect();

    let mut sum: u64 = 0;
    for i in 0..n {
        sum += a[i];
    }

    println!("{}", sum);
}