n = raw_input()
v = raw_input()
r = []
split_v = v.split()
for i in range(1, n):
 if i == 1: r.append (v[0])
 if i == 2: r.append (max([v[0], v[1]]))
 else:
  r.append(max([v[i-1], v[i-2] + v[i]]))
print r[n-1]