import sys
input=sys.stdin.readline

def main(args):
    N = int(input())
    A = list(map(int,input().split()))
    
    katamari = []
    kosu = 1#ある数字のかたまりに含まれる，その数字の個数
    prev = None#直前の値
    for a in A:
        if a == prev:
            kosu += 1
        else:
            katamari.append(kosu)
            prev = a
            kosu = 1
    katamari.append(kosu)
    
    katamari = katamari[1:]
    #print("katamari",katamari)
    
    if len(katamari) > 1:
        dp = [katamari[0],katamari[1]] + [0]*(len(katamari)-2)#その位置を採用したときの最大値
        #highest = [katamari[0],max(katamari[0],katamari[1])]
        for i in range(2,len(katamari)):
            dp[i] = max(dp[:i-1]) + katamari[i]
            #highest.append(max(dp[i],highest[i-2]))
            
        #print("dp",dp)
        #print('highest',highest)
        
        print(dp[-1])
    else:
        print(katamari[0])

if __name__ == '__main__':
    main(sys.argv[1:])