各位大佬此程序如何加上while循环

fanshu = input("请输入分数：")
fanshu = int(fanshu)
if 0<= fanshu <60:
print("D")
elif 60<= fanshu <80:
print("C")
elif 80<= fanshu <90:
print("B")
elif 90<= fanshu <100:
print("A")
elif fanshu == 100:
print("S!")
else:
print("数字非法")