fn digits_to_vec(digits: String) -> Vec<u32> {
    let mut result = Vec::new();
    for c in digits.chars() {
        match c.to_digit(10) {
            Some(v) => result.push(v),
            None => {}
        }
    }
    return result;
}

fn main() {
    let mut digits_string = String::new();
    std::io::stdin().read_line(&mut digits_string).expect("wtf?");
    let digits = digits_to_vec(digits_string);
    let length = digits.len();
    let halfway = length / 2;
    let mut compare_to = Vec::new();
    compare_to.extend(digits[halfway..length].iter().cloned());
    compare_to.extend(digits[0..halfway].iter().cloned());
    let mut result = 0;
    for (a, b) in digits.iter().zip(compare_to.iter()) {
        if a == b {
            result += a;
        }
    }
    println!("{}", result);
}