fn main() {
    let mut abs = String::new();
    std::io::stdin().read_line(&mut abs).ok();
    let abs: Vec<isize> = abs.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let mut a = abs[0];
    let b = abs[1];
    let s = abs[2];

    let mut result: isize = 0;
    if a == 0 {
        result += 1;
        a += 1;
    }
    if s <= a {
        result += a;
    } else if (a-s).abs() <= (b-s).abs() {
        result += (a-s).abs()+s.abs();
    } else {
        result += (b-s).abs()+(a-s).abs()+a.abs();
    }
    println!("{}", result);
}