N = int(input())
lsA = [int(input()) for i in range(N)]
lsA.sort()
ans = 1
now = lsA[0]
for i in range(1,N):
    if lsA[i]>lsA[i-1]+1:
        now = lsA[i]
    else:
        ans += 1
        now = lsA[i]
print(ans)