L = [int(input()) for i in range(int(input()))]
d = {}
for i in L:
d[i] = 1
ans = 4
for i in L:
for start in range(i-4,i+1):
cnt = 5
for j in range(5):
try:
d[start + j] +=1
d[start + j] -=1
cnt-=1
except:
continue
if cnt < ans:
ans = cnt
print(ans)