# Re2 : C++ is fun: [100]So you get a binary when running it you get a message to enter the flag. When entering somthing wrong it tells you to try again. However, since I know that the flag starts with "ALEXCTF{" I trief that and got the message "You should have the flag by now" then I thought that the original code might look somthing like this```c++#include <stdio.h>#include <string.h>using namespace std;int main () {  string flag="....";  string input;  cout << "Your flag: ";  cin >> input;   if (!flag.compare(0, input.size(), input))      cout<< "You should have the flag by now\n";    }  return 0;}```
Now I can try to bruteforce it by writing a small python script as following:
```python#!/usr/bin/python
import os
bin="~/Downloads/re2 ";char_set="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_{}";flag=""
while "}" not in flag:  for c in char_set:    flag_test=flag+c    p = os.popen(bin+flag_test,"r")    line = p.readline()    if "flag" in line:      flag=flag+c      print flag      break```
By running this script I got the flag `ALEXCTF{W3_L0v3_C_W1th_CL45535}`