n=int(input())
a=[int(i) for i in input().split()]+[0]*100

s=sum(a)
h=1
while (h+1)*(h+1)<=s:
    h+=1

p=0
for i in range(h-1):
    j=i+1
    if a[i]>j:  p+=a[i]-j
    k=2*h-i-2
    if a[k]>j:  p+=a[k]-j


c=h-1
if a[c]>h:  p+=a[c]-h

print(p)