temp = ''
results = []
for i in range(len(s)):
    if temp == '':
        temp = s[i]
    else:
        if  temp[-1] <= s[i]:
            temp += s[i]
        else:
            temp += s[i-1]
            results.append(temp)
            temp = ''
if not results:
    results.append(temp)
    print("Longest substring in alphabetical order is: " + results[0])
else:
    print("Longest substring in alphabetical order is: " + max(results, key=len))