N = int(input())
A = list(map(int, input().split()))

ans = 0
need = 0
flag = 0
for i in range(N):
    if A[i] <= N:
        continue

    need += 1
    #初回
    if flag == 0:
        ans += A[i]-N-1
        flag = 1
    else:
        ans += A[i] - A[i-1] - 1

ans += need
print(ans)