How many number of days they spent in their vacation?

Four friends planned to go on a vacation to a hill station.
During their vacation, they experienced 13 days of heavy snowfall. When it used to snow in the morning, the afternoon was clear and when it used to snow in the afternoon, the day was followed by a clear morning.

In total,
They had 11 clear mornings and 12 clear afternoons. How many number of days they spent in their vacation?