from collections import defaultdict

n = int(input())
P = list(map(int, input().split()))

G = defaultdict(int)
RG = defaultdict(int)
for i in range(n - 1):
    G[P[i]] = P[i + 1]
G[P[n - 1]] = None
for i in range(n - 1, 0, -1):
    RG[P[i]] = P[i - 1]
RG[P[0]] = None
ANS = []
for i in range(1, n + 1):
    nex = G[i]
    if nex is None:
        continue
    ANS.append(i)
    ANS.append(nex)
    new_nex = G[nex]
    G[i] = None
    G[nex] = None
    pre = RG[i]
    if pre is not None:
        G[pre] = new_nex
    if new_nex is not None:
        RG[new_nex] = pre
print(*ANS)