A1612.[COCI-2020-2021-contest5]#3 Po

Tinky Winky left a sequence of n zeroes in the Tubbytronic Superdome, and left for a walk with Dipsy. When he came back, he saw that a misdeed has been done. The sequence was changed, and Po was smiling mischeviously in the corner of the room.
Oh dear! Po, what have you done?! – asked Tinky Winky in horror.
I enhanced the sequence! – replied Po.
After cross-examination, it was established that Po did a number of enhancements on the sequence. In every enhancement, she took a segment of a sequence and increased all elements in the segment by some positive integer. Also, every two segments were either disjoint or one was completely contained in other.
How many enhancements have you done, Po? – Laa-Laa inquired.
I really don’t know! I’m only sure I did the minimum number of enhancements possible to get this sequence! – said Po exhaustedly.
Then it surely must be m! – proclaimed Noo-Noo. 1 What number did Noo-Noo say?

The first line contains an integer n (1 ≤ n ≤ 100 000), the length of the sequence.
The second line contains n nonnegative integers ai (0 ≤ ai ≤ 10^9), the sequence after Po’s enhancements.

Output m, the minimum possible number of enhancements.

In test cases worth 30 points, it holds 1 ≤ n ≤ 1000.

Clarification of the second example:
Po first increased all elements of the sequence by 2, and then increased the middle three by 1.