```
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) + "}")

```