#include<stdio.h>

typedef enum {MON, TUE, WED, THU, FRI, SAT, SUN} DayType;

DayType findNextDay(DayType day) {
  return (day+1) % 7;
}

DayType findPrevDay(DayType day) {
  return (day+6) % 7;
}

void printDay(DayType day) {
  switch(day) {
  case MON: printf("mon"); break;
  case TUE: printf("tue"); break;
  case WED: printf("wed"); break;
  case THU: printf("thu"); break;
  case FRI: printf("fri"); break;
  case SAT: printf("sat"); break;
  case SUN: printf("sun"); break;
  }
  printf("\n");
}

int main() {
  printDay(MON);
  printDay(findPrevDay(MON));
}