def route s
  c = 0
  s.strip.lines.map do |line|
    a,b = line.split(' ').map(&:to_i)[c..c.next]
    r,c = a.to_i>b.to_i ? [a,c] : [b,c.next]
    r
  end.inject(0){|s,n| s+n }
end

puts route("""
3
7 4
2 4 6
8 5 9 3
""")