n = int(input())
a = [int(input()) for _ in range(n)]
a.sort()
if n == 0:
    print(0)
    exit()
count = 1
current_max = a[0]
for i in range(1, n):
    if a[i] > current_max + 1:
        current_max = a[i]
    else:
        count += 1
        current_max = a[i]
print(count)