s = input()
ans = []
i = len(s) - 2
ans = [s[-1]]
while i >= 0:
    if s[i] < s[i + 1]:
        ans.append(s[i] * 2)
        i -= 1
        while i >= 0 and s[i] == s[i + 1]:
            ans.append(s[i] * 2)
            i -= 1
    else:
        ans.append(s[i])
        i -= 1
print(''.join(reversed(ans)))