Go: package main

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

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 500001), 500000)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func main() {
	fp := os.Stdin
	if len(os.Args) > 1 {
		fp, _ = os.Open(os.Args[1])
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(os.Stdout)

	n := getNextInt(scanner)

	g := make([][]int, n)
	ans := make([][]int, n)

	inf := 1 << 30
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		ans[i] = make([]int, n)
		for ii := 0; ii < n; ii++ {
			g[i][ii] = getNextInt(scanner)
			if g[i][ii] == -1 {
				g[i][ii] = inf
			}
			ans[i][ii] = -1
		}
	}

	im := make(IntMap, 1)

	im.increment(1)

	for len(im) < n {
		min := inf
		u := -1
		v := -1
		for i := range im {
			for ii := 0; ii < n; ii++ {
				if im.get(ii) != 0 {
					continue
				}
				if min > g[i][ii] {
					min = g[i][ii]
					u = i
					v = ii
				}
			}
		}
		im.increment(v)
		ans[u][v] = min
		ans[v][u] = min
	}

	sum := 0
	for i := 0; i < n-1; i++ {
		for ii := i + 1; ii < n; ii++ {
			if ans[i][ii] != -1 {
				sum += ans[i][ii]
			}
		}
	}

	fmt.Fprintln(writer, sum)
	writer.Flush()
}

// IntMap ...
type IntMap map[int]int

func (m IntMap) get(key int) int {
	if _, ok := m[key]; ok {
		return m[key]
	}
	return 0
}
func (m IntMap) increment(key int) {
	if _, ok := m[key]; ok == false {
		m[key] = 0
	}
	m[key]++
}

C++: #include<bits/stdc++.h>
using namespace std;
#define int long long
#define double long double
#define SZ(x) ((int)(x).size())
#define rep(i,n) for(int i=0;i<(n);++i)
#define fore(i,a) for(auto &i:a)
#define min(...) min({__VA_ARGS__})
#define max(...) max({__VA_ARGS__})
#define Yes cout << "Yes" << endl;
#define No cout << "No" << endl;
#define ALL(x) (x).begin(),(x).end()
signed _main(); signed main() { cin.tie(0); ios::sync_with_stdio(false); _main(); }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> using v = vector<T>;
template<class T> using vv = vector<v<T>>;
const int MOD=1e9+7;
const long long INF = 1LL << 60;
using P=pair<int,int>;


signed _main(){
  int n; cin >> n;
  vv<int> M(n,v<int>(n));
  rep(i,n)rep(j,n) cin >> M[i][j];
  v<int> color(n,0),d(n,INF),p(n,-1);
  d[0]=0;//TとV-Tをつなぐ辺で最も重みが小さいものの大きさ
  int u,minv,sum=0;

  while(1){
    minv=INF;
    u=-1;//確定した頂点
    rep(i,n){
      if(minv > d[i] && color[i] != 2){
        u=i;
        minv = d[i];
      }
    }
    if(u == -1) break;//更新無し
    color[u]=2;
    rep(v,n){
      if(color[v]!=2 && M[u][v]!=-1){
        if(d[v]>M[u][v]){
          d[v]=M[u][v];
          p[v]=u;
          color[v]=1;
        }
      }
    }
  }

  rep(i,n){
    if(p[i]!=-1) sum+=M[i][p[i]];
  }

  cout << sum << endl;

  return 0;
}

C++: #include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;

#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INF 2000000000

int x[10000][10000];
int color[10000];
int MIN[10000];
int sum;
int sum_min = INF;

int main() {
	int n, a, b, c;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> x[i][j];
		}
	}
	for (int i = 0; i < n; i++) {
		memset(MIN, 1, sizeof(MIN));
		b = INF;
		a = 1;
		color[i] = GRAY;
		MIN[i] = 0;
		while (a >= 1) {
			for (int j = 0; j < n; j++) {
				if (color[j] = GRAY) {
					if (b > MIN[j]) {
						b = MIN[j];
						c = j;
					}
				}
			}
			color[c] = BLACK;
			a -= 1;
			for (int j = 0; j < n; j++) {
				if (color[j] != BLACK && x[c][j] != -1) {
					if (color[i] == WHITE) {
						a += 1;
					}
					color[j] = GRAY;
					MIN[j] = min(x[c][j], MIN[j]);
				}
			}
		}
		sum = 0;
		for (int j = 0; j < n; j++) {
			sum += MIN[j];
		}
		sum_min = min(sum_min, sum);
	}
	cout << sum_min << endl;
	return 0;
}