prepare (1/3): 
finished

make (2/3): 
g++ -g -Wall -std=c++11 main.cpp -o main -O2
main.cpp: In function 'int main(int, char**)':
main.cpp:47:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < timetravelers.size(); i++) {
                     ~~^~~~~~~~~~~~~~~~~~~~~~
finished

clean (3/3): 
finished

all task finished, build successfully