foo.cc: In function 'void Work()':
foo.cc:63:28: error: no match for 'operator=' (operand types are 'std::basic_ostream<char>' and 'int')
         cout << last_ans = o_pos;
                            ^~~~~
In file included from /usr/include/c++/7/istream:39:0,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/ostream:402:7: note: candidate: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator=(std::basic_ostream<_CharT, _Traits>&&) [with _CharT = char; _Traits = std::char_traits<char>]
       operator=(basic_ostream&& __rhs)
       ^~~~~~~~
/usr/include/c++/7/ostream:402:7: note:   no known conversion for argument 1 from 'int' to 'std::basic_ostream<char>&&'
foo.cc:66:28: error: no match for 'operator=' (operand types are 'std::basic_ostream<char>' and 'int')
         cout << last_ans = 0;
                            ^
In file included from /usr/include/c++/7/istream:39:0,
                 from /usr/include/c++/7/sstream:38,
                 from /usr/include/c++/7/complex:45,
                 from /usr/include/c++/7/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:52,
                 from foo.cc:1:
/usr/include/c++/7/ostream:402:7: note: candidate: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator=(std::basic_ostream<_CharT, _Traits>&&) [with _CharT = char; _Traits = std::char_traits<char>]
       operator=(basic_ostream&& __rhs)
       ^~~~~~~~
/usr/include/c++/7/ostream:402:7: note:   no known conversion for argument 1 from 'int' to 'std::basic_ostream<char>&&'

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。