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while True:
_E5_88_86_E6_95_B0 = float(input('请输入成绩：'))
if (100 >= _E5_88_86_E6_95_B0 and _E5_88_86_E6_95_B0 >= 90):
print('A')
elif (90 >= _E5_88_86_E6_95_B0 and _E5_88_86_E6_95_B0 >= 80):
print('B')
elif (80 >= _E5_88_86_E6_95_B0 and _E5_88_86_E6_95_B0 >= 60):
print('c')
elif (60 >= _E5_88_86_E6_95_B0 and _E5_88_86_E6_95_B0 >= 20):
print('D')
elif (20 >= _E5_88_86_E6_95_B0 and _E5_88_86_E6_95_B0 >= 0):
print('E')
else:
print('输入有误！请重新输入!')