# encoding: utf-8

class UFSet
  def initialize(sz)
    @sz = sz
    @par = [0] * sz
    (0..sz - 1).each { |idx| @par[idx] = idx}
  end

  def find(x)
    if @par[x] == x
      x
    else
      @par[x] = find(@par[x])
    end
  end

  def same(x, y)
    find(x) == find(y)
  end

  def unite(x, y)
    fx = find(x)
    fy = find(y)
    @par[fx] = fy if fx != fy
  end
end

class Graph
  def initialize(v)
    @v = v
    @edge = []
  end

  def add_edge(u, v, w)
    @edge << { from: u, to: v, weight: w}
  end

  def mst_kruskal
    ans = 0
    @edge = @edge.sort_by { |x| x[:weight]}
    ufset = UFSet.new(@v)
    @edge.each do |ee|
      u, v, c = ee[:from], ee[:to], ee[:weight]
      if not ufset.same(u, v)
        ans += c
        ufset.unite(u, v)
      else
        next
      end
    end
    ans
  end
end

def main
  n = gets.rstrip.to_i
  g = Graph.new(n)
  (0..n - 1).each do |row|
    r = gets.lstrip.rstrip.split(/\s/).map(&:to_i)
    r.each_with_index do |node, idx|
      g.add_edge(row, idx, node) if node >= 0
    end
  end
  puts g.mst_kruskal
end

main