n = int(input())
p = list(map(int, input().split()))
p = list(reversed(p))
takeda = [x for x in range(1, n+1)]
ansT, ansS = 0, 0

for i in range(n):
	score = n-i
	tmp = p[i]
	while True:
		tmp += 1
		if tmp in takeda:
			ansT += score
			takeda.remove(tmp)
			break
		if tmp > max(takeda):
			if p[i] in takeda:
				takeda = takeda[1:]
			else:
				ansS += score
				takeda = takeda[1:]
			break
print(ansT - ansS)