N = int(input())
A = list(map(int,input().split()))
ans = 0

flag = True
while flag:
  flag = False
  for i in range(N):
    for j in range(i+1,N):
      if A[i]-A[j]==1:
        A[i],A[j] = A[j],A[i]
        flag = True
        ans += 1
print (ans)

"""
swap test
"""