N = gets.chomp.to_i
p = gets.chomp.split(" ").map(&:to_i)
s = p.inject(:*)
f = 1

def moji(s)
  zzz = s.to_s
  sl = s.to_s.length
  return zzz, sl
end

zzz, sl = moji(s)

while(f)
  if sl > 1
    yyy = 0
    for i in 0...sl
      yyy +=zzz[i].to_i
    end
    zzz, sl= moji(yyy)
  else
    yyy = zzz[0]
    f = nil
  end
end
p yyy.to_i