Pikachu and Stones

Charizard and Dragonite have a Pokemon tournament scheduled today. In order to keep Pikachu busy they gave him a task. He is given $N$ piles of stones with where $i^{th}$ pile has $A_i$ stones, and his task is to make a peak from the piles of stones without moving stones from one pile to another. Collection of piles make a peak if the no of stones in the pile is strictly increasing from inde