The flag is solved by running the program:
with C++11 g++ -std=c++11 solve.cpp -o solve
./solve > combos.txt
then you open combos.txt
Use the search function in your code editor to look at the combo @ S
@ S : KkNURntQQVlfQVRURU5USU9OX1RPX1RIRV9ERVRBSUxTfQ==
decode this encoded string: KkNURntQQVlfQVRURU5USU9OX1RPX1RIRV9ERVRBSUxTfQ==
*CTF{PAY_ATTENTION_TO_THE_DETAILS}