fn main() {
    let n: usize = read();
    assert!(n % 2 == 0);
    let mut nums: Vec<usize> = read_vec();
    for p in old_maid(&mut nums) {
        print!("{} ", p);
    }
    print!("\n");
}

fn old_maid(nums: &mut[usize]) -> Vec<usize> {
    assert_eq!(nums.len() % 2, 0);
    let n = nums.len();
    let mut rev = vec![usize::MAX; n];
    for p in nums.iter_mut() {
        *p = *p - 1;
    }
    for (i, p) in nums.iter().enumerate() {
        rev[*p] = i;
    }
    let mut ret = Vec::new();
    let mut min = 0;
    for _ in 0..n / 2 {
        while rev[min] >= nums.len() - 1 {
            min += 1;
            assert!(min < nums.len());
        }
        let mut n_idx = rev[min] + 1;
        while nums[n_idx] >= rev.len() || rev[nums[n_idx]] >= nums.len() {
            n_idx += 1;
            assert!(n_idx < nums.len());
        }
        let next = nums[n_idx];
        rev[min] = usize::MAX;
        rev[next] = usize::MAX;
        while rev.last().is_some_and(|i| *i == usize::MAX) {
            rev.pop();
        }
        ret.push(min + 1);
        ret.push(next + 1);
    }
    ret
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

fn read_vec2<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

#[cfg(test)]
mod test {
    use super::old_maid;

    #[test]
    fn test() {
        assert_eq!(old_maid(&mut vec![3, 2, 4, 1]), vec![2, 4, 3, 1]);
        assert_eq!(old_maid(&mut vec![4,6,3,2,8,5,7,1]),  vec![2,8,3,5,4,6,7,1]);
    }
}