Movie Festival-CSES problem

Hi, have been trying to solve this problem. I am only missing one test case but that is really big, therefore I am not able to debug my code now. Can you please tell me what am I am doing wrong.

problem link: https://cses.fi/problemset/task/1629
code link: https://cses.fi/paste/c3b2a6ef0510a27812d5e2/

Algorithm

sort the array of <start_time,end_time> by end_time in asc order.
inititiialize prev = 0, next = 1, movies_watched = 1;

int next= 1, prev = 0;
while (next <= n - 1 && prev <= n - 1)
{   // if ending time of prev movie <= start_time of next movie, I can watch next movie
	if (movie_times[prev].second <= movie_times[next].first) 
	{
		movies_watched++;
		next++;
		prev++;
	}

	else
 // I can't watch next movie, only increment prev
	{ 
		prev++;
	}
}