import heapq


n = int(input())
a = [int(input()) for i in range(n)]


a.sort()
hq = []
for i in range(n):
    if not hq:
        heapq.heappush(hq, a[i])
    else:
        top = hq[0]
        if abs(top - a[i]) > 1:
            heapq.heappop(hq)
            heapq.heappush(hq, a[i])
        else:
            heapq.heappush(hq, a[i])
print(len(hq))