import heapq
N = int(input())
A = list(map(int,input().split()))
A = A[::-1]

ans = 0
count = 1
free = []
while(A):
    while(free and free[0] == count):
        heapq.heappop(free)
        count += 1
    if(A[-1] == count):
        A.pop()
        count += 1
    else:
        ans += 1
        heapq.heappush(free,A.pop())
print(ans)