Go: package main

import (
	"sort"
	"bufio"
	"os"
	"fmt"
	"strconv"
)

// Define disjoint-set forests

type vertexNo int

type vertex struct {
	number vertexNo
	rank int
	parent *vertex
}

func makeSet(number vertexNo) vertex {
	return vertex {
		number: number,
		rank: 0,
		parent: nil,
	}
}

func union(x, y *vertex) *vertex {
	return link(findSet(x), findSet(y))
}

func link(x, y *vertex) *vertex {
	if x.rank > y.rank {
		y.parent = x
		return x
	} else {
		x.parent = y
		if x.rank == y.rank {
			y.rank += 1
		}
		return y
	}
}

func findSet(v *vertex) *vertex {
	if v.parent == nil {
		return v
	}
	v.parent = findSet(v.parent)
	return v.parent
}

// Function to calculate minimum spanning tree

type matrix [][]int

type edge struct {
	one vertexNo
	two vertexNo
	weight int
}

const(
	MAX_VERTICES = 100
)

func newEdgesFromMatrix(matrix matrix) []edge {
	edges := make([]edge, 0, MAX_VERTICES * MAX_VERTICES)

	for i := 0; i < len(matrix); i++ {
		row := matrix[i]
		for j := i; j < len(row); j++ {
			if row[j] >= 0 {
				edge := edge{one: vertexNo(i+1), two: vertexNo(j+1), weight: row[j]}
				edges = append(edges, edge)
			}
		}
	}

	return edges
}

func solve(matrix matrix) int {
	nVertices := len(matrix)

	// initialize vertices
	vertices := make([]vertex, nVertices)
	for i := 0; i < nVertices; i++ {
		vertices[i] = makeSet(vertexNo(i+1))
	}

	// prepare edges sorted in the ascending order of weight
	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	unionCount := 0
	weightSum := 0
	for unionCount < nVertices-1 {
		for i := 0; i < len(edges); i++ {
			edge := edges[i]
			v1 := &vertices[edge.one-1]
			v2 := &vertices[edge.two-1]
			rep1 := findSet(v1)
			rep2 := findSet(v2)
			if rep1.number == rep2.number {
				continue
			}
			union(rep1, rep2)
			edges = append(edges[0:i], edges[i+1:]...)
			weightSum += edge.weight
			unionCount++
			break
		}
	}

	return weightSum
}

// main

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	n, err := nextInt(sc)
	if err != nil {
		panic(err)
	}

	matrix := parseMatrix(n, sc)

	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	fmt.Println(solve(matrix))
}

func parseMatrix(n int, sc *bufio.Scanner) [][]int {
	matrix := make([][]int, n)
	for i := 0; i < n; i++ {
		matrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			x, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			matrix[i][j] = x
		}
	}
	return matrix
}

func nextText(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

func nextInt(sc *bufio.Scanner) (int, error) {
	return strconv.Atoi(nextText(sc))
}

C++: #include <cstdio>
#include <map>
#include <algorithm>

#define rep(i, n) for(int i = 0; i < (n); ++i)

using namespace std;

int n;
int g[100][100];

vector<pair<int, int> > computeSpanningTree(std::vector<pair<int, pair<int, int> > >& edges){
  class UnionFind{
  public:
    UnionFind(int n){
      for(int i = 0; i < n; ++i){
        parent.push_back(i);
      }
      rank.resize(n, 0);
    }

    bool same(int a, int b){
      return find(a) == find(b);
    }

    void unite(int a, int b){
      int p = find(a), q = find(b);

      // assume that p != q

      if(rank[p] > rank[q]){
        parent[q] = p;
      }
      else{
        parent[p] = q;
        
        if(rank[p] == rank[q]){
          ++rank[q];
        }
      }
    }

  private:
    int find(int a){
      return a == parent[a] ? a : parent[a] = find(parent[a]);
    }

  private:
    vector<int> parent, rank;
  };

  class Indexer{
  public:
    int add(int p){
      if(indexer.find(p) == indexer.end()){
        int new_id = indexer.size();
        indexer[p] = new_id;
      }
      return indexer[p];
    }

  private:
    std::map<int, int> indexer;
  };

  sort(edges.begin(), edges.end());

  Indexer id;
  UnionFind uf(edges.size() * 2);

  vector<pair<int, int> > result;
  for(int i = 0; i < edges.size(); ++i){
    int from = edges[i].second.first;
    int to = edges[i].second.second;

    int a = id.add(from);
    int b = id.add(to);

    if(!uf.same(a, b)){
      result.push_back(make_pair(from, to));
      uf.unite(a, b);
    }
  }

  return result;
}

int main(){
	scanf("%d", &n);
	rep(i, n){
		rep(j, n){
			scanf("%d", &g[i][j]);
		}
	}

	std::vector<pair<int, pair<int, int> > > gr;
	rep(i, n){
		for(int j = i; j < n; ++j){
			if(g[i][j] != -1){
				gr.push_back(make_pair(g[i][j], make_pair(i, j)));
			}
		}
	}
	vector<pair<int, int> > edge = computeSpanningTree(gr);
	int s = 0;
	rep(i, edge.size()){
		s += g[edge[i].first][edge[i].second];
	}
	printf("%d\n", s);
	return 0;
}