count_room = int(input())
tea = list(map(int,input().split()))
max_happy = 0
for i in range(count_room-1):
if ((tea[i] - 1)*(tea[i+1] - 1)) > max_happy:
max_happy = (tea[i] - 1)*(tea[i+1] - 1)
print(max_happy)
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