jabloki = gets.chomp
j100 = jabloki.count("1") # количество 100-граммовых яблочек
j200 = jabloki.count("2") # 200-граммовые
weight = j100 + j200*2 	  # суммарный вес
# дальше сами разберетесь, все просто
divider = (j100 > 2) && (j200 > 2) ? 2 : 1 
divider2 = (j100 == 0) && (j200 > 2) ? 2 : 1
divided_weight = weight / divider / divider2
puts (weight.even?) && (divided_weight.even? || (divided_weight == 0)) ? 'YES' : 'NO'

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MTAwIDIwMCAxMDAgMjAw

100 200 100 200