N = int(input())
l =[]

for i in range(N):
    l.append(int(input()))

l.sort()
ans = 0
for i in range(N-2):
    if l[i + 1] - l[i] <= 1:
        ans +=1

if l[N-1] - l[N-2] <= 1:
    ans += 2
else:
    ans += 1

print(ans)