"""
[15966: 군계일학](https://www.acmicpc.net/problem/15966)
Tier: Silver 1
Category: dp
"""
import sys
inp = lambda : sys.stdin.readline().rstrip()
mii = lambda : [*map(int,inp().split())]
MX = 1000001
def solve():
inp()
l = mii()
dp = [0] * MX
for i in l:
dp[i] = dp[i - 1] + 1
return max(dp)
if __name__ == "__main__":
print(solve())