#include<stdio.h>
#include<stdlib.h>

int is_leap_year(int year){
    if((year - 2000)%400==0)
        return 1;
    else if((year - 2000)%100 == 0)
        return 0;
    else if((year - 2000)%4 == 0)
        return 1;
    else
        return 0;
}

int cal_week_day(int year, int month, int day){
    const int year2000_start_week_day = 5;//0-base, 2000/1/1 is Saturday
    int year_start_week_day = 0;//week day of JAN 1st
    int week_day = 0;
    int common_year_week_day_offset[12] = {0,3,3,6,1,4,6,2,5,0,3,5};
    int leap_year_week_day_offset[12]   = {0,3,4,0,2,5,0,3,6,1,4,6};

    //find the start week day of the year
    year_start_week_day = year2000_start_week_day;
    if(year > 2000){
        year_start_week_day += (year - 2000)*365;
        year_start_week_day += 1;//because 1/1-12/31 is 365 days, the 1/1 of next year is the 366th day.
    }
    if(year - 2000 >= 4){
        year_start_week_day += (year - 2000) / 4;
    }
    if(year - 2000 >= 100){
        year_start_week_day -= (year - 2000) / 100;
    }
    if(year - 2000 >= 400){
        year_start_week_day += (year - 2000) / 400;
    }
    year_start_week_day %= 7;

    //find week day
    if(is_leap_year(year)){
        week_day = (year_start_week_day + leap_year_week_day_offset[month-1] + (day-1))%7;
    }else{
        week_day = (year_start_week_day + common_year_week_day_offset[month-1] + (day-1))%7;
    }

    return week_day;
}

int main(int argc, char* argv[]){
    int year = atoi(argv[1]);
    int month = atoi(argv[2]);
    int day = atoi(argv[3]);
    //printf("%d/%d/%d week day(1-7):%d\n",year,month,day,cal_week_day(year,month,day)+1);
    printf("%d/%d/%d week day(0-6):%d\n",year,month,day,cal_week_day(year,month,day));
}