#include <iostream>

class StopWatch {
public:
    StopWatch();
    void start();
    void stop();
private:
    bool running;
    double f;
    long long start_time;
    long long total_time;
    long long getExecutionTime() const;
    void printError() const;
    friend std::ostream& operator<<(std::ostream& o, const StopWatch& sw);
};