N=int(input())
P=list(map(lambda x:x-1,map(int, input().split())))
Q=[0]*N
for i,p in enumerate(P):
    Q[p]=i
res=0
for n in range(N)[::-1]:
    res=max((n+1)*(n+2)//2 - 2*(Q[n]+1),res)
print(res)