N = int(input())
P = list(map(int, input().split())) + ["$"]
nex = [-1] * (N + 1)
pre = [-1] * (N + 1)
for i in range(N):
    nex[P[i]] = P[i + 1]
    pre[P[i]] = P[i - 1]
    
ans = []
S = set()
for i in range(1, N):
    if nex[i] == "$" or i in S:
        continue
    ans.append(i)
    ans.append(nex[i])
    S.add(i)
    S.add(nex[i])
    p = pre[i]
    n = nex[nex[i]]
    if p != "$":
        nex[p] = n
    if n != "$":
        pre[n] = p
    
print(*ans)