The trap

The naive solution is "sort and pick a[n-2]". That works for distinct values, but breaks on [5, 5, 4] where a[n-2] is 5, which is the largest, not the second largest. And sorting is O(n log n) for a problem that should be O(n).

The right way

Keep two variables: largest and second. Walk the array once. For each value x:

• If x > largest: the old largest just got demoted. second = largest, largest = x.
• Else if x < largest and x > second: update second only.
• Else: ignore.

The x < largest check is the part beginners forget — without it, duplicates of the largest also overwrite second.

largest = -inf
second  = -inf
for x in a:
    if x > largest:
        second = largest
        largest = x
    elif x < largest and x > second:
        second = x

If at the end second is still -inf, there was no second distinct value — output -1.

Input and output

Line one is N. Line two is N space-separated integers. Print the second largest distinct value, or -1.