def main():
    _, *l = open(0)
    q = []
    while l:
        a = l[:2]
        for i in range(len(l) - 1):
            if (b := l[i, i + 2]) < a:
                a = b
        q += a
        del l[i:i + 2]
    print(q)

if __name__ == "__main__":
    main()