C++ 11:

/usr/bin/g++ -O2 -static -DONLINE_JUDGE -std=c++11 main.cpp grader.cpp
a.out 

C++ 14:

/usr/bin/g++ -O2 -static -DONLINE_JUDGE -std=c++14 main.cpp grader.cpp
a.out 

C++ 17:

/usr/bin/g++ -O2 -static -DONLINE_JUDGE -std=c++17 main.cpp grader.cpp
a.out