import itertools
n = int(input())
P = list(map(int,input().split()))
ans = 0
use = [0]*(n+1)
score = 0
for i in range(n)[::-1]:
    p = P[i]
    if p == n:
        score -= i+1
        use[1] = 1
    else:
        score += i+1
        use[p+1] = 1
print(max(ans,score))