#include <iostream>
	#include <fstream>
	
	using namespace std;
	
	class Logger {
	public:
	    Logger(ostream& os) : os_(os), curIndentLevel_(0) {}
	    void increaseLevel() { ++curIndentLevel_; }
	    void decreaseLevel() { --curIndentLevel_; }
	    
	private:
	    template<typename T> friend ostream& operator<<(Logger&, T);
	
	    ostream& os_;
	    int curIndentLevel_;
	};
	
	template<typename T> 
	ostream& operator<<(Logger& log, T op) {
		for(int i = 0; i < log.curIndentLevel_ * 4; ++i) {
			log.os_ << ' ';
		}
		log.os_ << op;
		return log.os_;
	}
	
	int main() {
		Logger log(cout);
		
		log.increaseLevel();
		log << "Hello World!" << endl;
		log.decreaseLevel();
		log << "Hello World!" << endl;
		return 0;
	}