```def decrypt(c):    m = ''    for i in range(len(c)):        ch = c[i]        if not ch.isalpha():            dch = ch        else:            chi = (ord(ch) - 0x41) % 26            dch = chr((chi - i) % 26 + 0x41)        m += dch    return m
if __name__ == '__main__':    ciphertext = "DJF_CTA_SWYH_NPDKK_MBZ_QPHTIGPMZY_KRZSQE?!_ZL_CN_PGLIMCU_YU_KJODME_RYGZXL"    print("Flag: HTB{" + decrypt(ciphertext) + "}")
```