n = int(input())

p = list(map(int,input().split()))
use = [True] * (n + 2)
use[0] = False
use[n + 1] = False
ans = 0
usemin = 1
for i in range(n - 1, -1, -1):
    if use[p[i] + 1]:
        use[p[i] + 1] = False
        ans += i + 1
    else:
        use[usemin] = False
        usemin += 1
        if usemin < p[i]:
            ans -= i + 1
    
print(ans)