if s_former.to_i.between?(01,12 ) && s_latter.to_i.between?(01, 12)
    puts "AMBIGUOS"
end

if s_former.to_i.between?(01,12 ) && ( s_latter.to_i.between?(13, 99) || s_latter.to_i == 00 )
    puts "MMYY"
end

if s_latter.to_i.between?(01,12 ) && ( s_former.to_i.between?(13, 99) || s_former.to_i == 00 )
    puts "YYMM"
end

if ( s_former.to_i.between?(13, 99) || s_former.to_i == 00 ) && ( s_latter.to_i.between?(13, 99) || s_latter.to_i == 00 )
    puts "NA"
end