poj2080 110ms 求日期

求日期和星期，不查怎么知道2000.1.1是星期六呢

#include<cstdio>
using namespace std;
//2000.1.1 星期六
//暴力吧，想不出什么捷径
bool is_leapyear(int n)
{
    return ((n%4==0&&n%100!=0)||(n%400==0));
}
char week[10][10]= {"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};
int month[20] = {0,31,28,31,30,31,30,31,31,30,31,30,31};
int main()
{
    int n;
    int year,m,day,w;
    while(scanf("%d",&n)&&n!=-1)
    {
        year = 2000,m = 1,day = 1,w = 6;
        w = (w+n)%7;
        while(n>365)
        {
            n -= 365;
            if(is_leapyear(year))
                n--;
            year++;
        }
        while(n--)
        {
            if(is_leapyear(year))
                month[2] = 29;
            else
                month[2] = 28;
            day++;
            if(day>month[m])
            {
                day = 1;
                m++;
                if(m>12)
                {
                    m = 1;
                    year++;
                }
            }
        }
        printf("%d-%02d-%02d %s\n",year,m,day,week[w]);
    }
    return 0;
}