Mini Calendar C

Hello everyone, I am doing the C mini calendar project.
The code does not give me errors, only that I have been searching for more than 2 hours for an error that does not give me the correct answer.
In step 30 of the project I verify that the code is working correctly but:
input: “12 31 2019 367 ” → should output “1 1 2021”.
But i am getting on and on the output: “1 1 2020”.

If you could help me I would be very grateful to you.
Thank you.
Postscript: I’m from Colombia that’s why some prints are in Spanish.

#include <stdio.h>
#include <stdbool.h>
bool is_leap_year(int year) {
  if (year % 4 != 0) {
    return false;
  } else if (year % 100 != 0) {
    return true;
  } else if (year % 400 != 0) {
    return false;
  } else {
    return true;
  }
}
int days_in_month[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

void add_days_to_date(int* mm, int* dd, int* yy, int days_left_to_add) {
  int days_left_in_month = days_in_month[*mm] - *dd; 
  while (days_left_in_month > 0) {
    if (days_in_month[2] && is_leap_year(*yy) == true) {
      days_left_in_month++;
    }
  }
  if (days_left_to_add > days_left_in_month) {
    days_left_to_add -= days_left_in_month + 1;
    *dd = 1;
    if (*mm == 12) {
      *mm = 1;
      *yy = *yy +1;
      } else {
        *mm = *mm + 1;
      }
    } else {
    *dd += days_left_to_add;
    days_left_to_add = 0;
  }
}
int main() {
  int year;
  printf("Elija un año entre 1800 y 10000: ");
  scanf("%i", &year);
  is_leap_year(year);
  if (is_leap_year(year) == true) {
    printf("Es año bisiesto\n");
  } else {
    printf("No es bisiesto\n");
  }
  
  int mm, dd, yy, days_left_to_add;
  printf("Please enter a date between the years 1800 and 10000 in the format mm dd yy and provide the number of days to add to this date: ");
  scanf("%i%i%i%i", &mm, &dd, &yy, &days_left_to_add);
  add_days_to_date(&mm, &dd, &yy, days_left_to_add);
  printf("%i %i %i\n", mm, dd, yy);
}