初学python：输入某年某月某日，判断这一天是这一年的第几天

if __name__=="__main__":
    a=[[31,28,31,30,31,30,31,31,30,31,30,31],[31,29,31,30,31,30,31,31,30,31,30,31]]
    year=int(input("请输入需要判断的年："))
    month = int(input("请输入需要判断的月："))
    day = int(input("请输入需要判断的日："))
    sum=0
    if (year%4==0 and year%100!=0)or year%400==0:
        for i in range(1,month):
            sum=sum+a[1][i]
    else:
        for i in range(1,month):
            sum=sum+a[0][i]
    sum=sum+day
    print("{}年{}月{}日是这一年的第：{}天".format(year,month,day,sum))