N = input()
M = len(N)
dp = [0] * (1<<M)
def isCww(i,j,k):
	return N[i] != N[j] and N[j] == N[k]
for s in range(1<<M):
	for i in range(M):
		if (s>>i)&1==1:
			continue
		for j in range(i + 1,M):
			if (s>>j)&1==1:
				continue
			for k in range(j + 1,M):
				if (s>>k)&1==1:
					continue
				if not isCww(i,j,k):
					continue
				next = (1<<i)|(1<<j)|(1<<k)
				next |= s
				v = int(N[i]+N[j]+N[k])
				dp[next] = max(dp[next],dp[s] + v)
print(max(dp))