写一段python代码：从上到下读取excel中B列4行到30行的数据，当出现值为“FAIL”时，输出它对应的A列的值。

import openpyxl

# 打开Excel文件
workbook = openpyxl.load_workbook('example.xlsx')

# 选择要操作的Sheet
sheet = workbook['Sheet1']

# 读取B列4-30行的数据，检查是否存在“FAIL”
for row in sheet.iter_rows(min_row=4, max_row=30, min_col=2, max_col=2):
cell_value = row[0].value
if cell_value == "FAIL":
# 如果出现“FAIL”，输出对应的A列的值
row_num = row[0].row
a_cell = sheet.cell(row=row_num, column=1)
a_value = a_cell.value
print(f"出现了FAIL，对应的A列的值为{a_value}")