In file included from /in/Compile/check.cpp:7:
/in/sokoban.hpp:139:56: error: implicit conversion changes signedness: 'int' to 'std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::size_type' (aka 'unsigned long') [-Werror,-Wsign-conversion]
                bool loop = check_loop(new_path.substr(last_move));
                                                ~~~~~~ ^~~~~~~~~
1 error generated.
/in/Compile/Makefile:16: recipe for target 'main' failed
make: *** [main] Error 1