#include <stdio.h>

int birthdayDay(int days, int month, int year);

int main(int argc, char const *argv[]) {

  birthdayDay(31,1,2018);

  return 0;
}

int birthdayDay(int days, int month, int year){

  if (month == 1){
    year -= 1;
    month = 13;
  }
  if (month == 2){
    year -= 1;
    month = 14;
  }

  int k = (year % 100);
  int j = (year / 100);

  int h1 = days +
          ( (13 * (month + 1) ) / 5) +
          k +
          ( k / 4 ) +
          ( j / 4 ) +
          ( 5 * j);

  int h = h1 % 7;

  switch (h) {
    case 0 : printf("You were born on Saturday"); break;
    case 1 : printf("You were born on Sunday"); break;
    case 2 : printf("You were born on Monday"); break;
    case 3 : printf("You were born on Tuesday"); break;
    case 4 : printf("You were born on Wednesday"); break;
    case 5 : printf("You were born on Thursday"); break;
    case 6 : printf("You were born on Friday"); break;
  }

  return 0;

}