/in/foo.cc: In function 'int main()':
/in/foo.cc:19:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (st.size() > ans)
       ~~~~~~~~~~^~~~~
/in/foo.cc:12:16: warning: variable 'flag' set but not used [-Wunused-but-set-variable]
  int i, ans=0, flag=0;
                ^~~~