The problem says :"the input contains a single LINE".
LINE is assumed to end with '\n' symbol,and I got TLE writing

cin.get(c);
while(c!='\n')
{...cin.get(c);}

then I changed this to
while(cin>>c) and got AC,but this kind of input ends with EOF character,NOT with '\n'!
Admins,please fix this!

Where have you read that "LINE is assumed to end with '\n' symbol"??? Is in written in Wikipedia or any other respectable resource?
Line is just a set of symbols in the input file, so all stuff for this problem is correct.

OK. Now all tests contain lines ending with '\n'.

Actually a LINE is not supposed to end with '\n'. What the term "Single LINE" really implies is that there are no printable characters AFTER '\n' symbol IF the latter exists.