from collections import defaultdict,deque
import sys,heapq,bisect,math,itertools,string,queue,copy,time
sys.setrecursionlimit(10**8)
INF = float('inf')
mod = 10**9+7
eps = 10**-7
def inp(): return int(sys.stdin.readline())
def inpl(): return list(map(int, sys.stdin.readline().split()))
def inpl_str(): return list(sys.stdin.readline().split())

N = inp()
AA = inpl()


tmpl = []
ba = -1
for a in AA:
    if ba == a:
        tmpl[-1] += 1
    else:
        tmpl.append(1)
    ba = a

L = len(tmpl)

# print(tmpl)

DP = [0]*L

if L == 1:
    print(tmpl[0])
    sys.exit()
elif L == 2:
    print(sum(tmpl)-1)
    sys.exit()

for i,x in enumerate(tmpl):
    if i == 0:
        DP[i] = x
    else:
        DP[i] = max(DP[i-1] + x-1, DP[i-2] + x + max(0,tmpl[i-1]-2))


# print(DP)
print(DP[-1])