n = int(input())
s, t = [], []
for i in range(n):
    te, mp = input().split()
    s.append(te)
    t.append(mp)

ans = ''
for i in range(n):
    if s[i] == '0':
        ans += t[i]
for i in range(n - 1, -1, -1):
    if s[i] == '1':
        ans += t[i]

print(ans)