Collection was modified exception

I saw some pretty strange solutions for this problem, most of all, ones which involve a "helper" list to store the items to remove... this of course is overkill (memory and cpu wise - think of collections with a million items ...)

Here's how to do it:

for (int i = pageList.Count; i-- > 0; )
{
    if (itemsToRemoveList.Contains(mainList[i]))
        mainList.RemoveAt(i);
}