fn main() {
    let mut a : Vec<usize> = input_vec();
    let xor = a.iter().fold(0,|acc,&v|acc^v);
    println!("{}", xor);
}
#[allow(dead_code)] fn input<T: std::str::FromStr>() -> T { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); s.trim().parse().ok().unwrap() } #[allow(dead_code)] fn input_t<T: std::str::FromStr, U: std::str::FromStr>() -> (T, U) { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); let s = s.trim().split_whitespace().collect::<Vec<&str>>(); (s[0].parse().ok().unwrap(), s[1].parse().ok().unwrap()) } #[allow(dead_code)] fn input_t3<T1: std::str::FromStr, T2: std::str::FromStr, T3: std::str::FromStr>() -> (T1, T2, T3) { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); let s = s.trim().split_whitespace().collect::<Vec<&str>>(); (s[0].parse().ok().unwrap(), s[1].parse().ok().unwrap(), s[2].parse().ok().unwrap()) } #[allow(dead_code)] fn input_t4<T1: std::str::FromStr, T2: std::str::FromStr, T3: std::str::FromStr, T4: std::str::FromStr>() -> (T1, T2, T3, T4) { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); let s = s.trim().split_whitespace().collect::<Vec<&str>>(); (s[0].parse().ok().unwrap(), s[1].parse().ok().unwrap(), s[2].parse().ok().unwrap(), s[3].parse().ok().unwrap()) } #[allow(dead_code)] fn input_t5<T1: std::str::FromStr, T2: std::str::FromStr, T3: std::str::FromStr, T4: std::str::FromStr, T5: std::str::FromStr>() -> (T1, T2, T3, T4, T5) { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); let s = s.trim().split_whitespace().collect::<Vec<&str>>(); (s[0].parse().ok().unwrap(), s[1].parse().ok().unwrap(), s[2].parse().ok().unwrap(), s[3].parse().ok().unwrap(), s[4].parse().ok().unwrap()) } #[allow(dead_code)] fn input_vec<T: std::str::FromStr>() -> Vec<T> { let mut s = String::new(); std::io::stdin().read_line(&mut s).ok(); s.trim().split_whitespace().map(|s| s.parse().ok().unwrap()).collect() }