import sys
readline=sys.stdin.readline
write=sys.stdout.write
from math import gcd as GCD
import math

N=int(readline())
A=[int(readline()) for i in range(N)]
A.sort()
if any(A[i+1]-A[i]==1 for i in range(N-1)):
    ans=2
else:
    ans=1
print(ans)