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def factorial( integer ):
#5=5*4*3*2*1
#integer*(integer-1)*(integer-1)-1
    temp =1
    if isinstance( integer, int):
        while integet and integer>0:
            temp = temp*integer
            integer -=1
        return temp
    else:
        print( '输入有误' )
integer = int( input( '请输入一个正整数:' )
factorial( integer)
print( integer,'的阶乘是', factorial( integer ))