Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

const INF = 1 << 60

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N := sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < N; i++ {
		G[i] = make([]int, N)
		for j := 0; j < N; j++ {
			G[i][j] = sc.nextInt()
		}
	}
	d := make([]int, N)
	for i := 0; i < N; i++ {
		d[i] = INF
	}
	seen := make([]bool, N)
	d[0] = 0
	ans := 0
	for {
		cur := 0
		minCost := INF
		for i := 0; i < N; i++ {
			if !seen[i] && d[i] < minCost {
				minCost = d[i]
				cur = i
			}
		}
		if minCost == INF {
			break
		}
		seen[cur] = true
		ans += d[cur]
		for i := 0; i < N; i++ {
			cost := G[cur][i]
			if cost != -1 && cost < d[i] {
				d[i] = cost
			}
		}
	}

	fmt.Fprintln(wtr, ans)
	wtr.Flush()
}

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

typedef long long ll;

#define MAX_V 100
#define INF int(1e9)

// g : ??°??????, V : g???????????°, s : ????????????????????????
int Prim (int g[MAX_V + 1][MAX_V + 1], int V, int s) {
    ll ret = 0, min_, nxtv, v = s, size_;
    // bool used[V] = {false}; // c++11??????
    bool used[V]; memset(used, 0, sizeof(used)); // c++11??\???
    vector<int> usedv;
    usedv.push_back(s);
    used[s] = true;

    while (usedv.size() < V) {
        min_ = INF;
        size_ = usedv.size();

        // ?????¨???????????????????????°?????????????????\?¶????????????????????°????????????¢???
        for (int i = 0; i < size_; ++i) {
            for (int j = 0; j < V; ++j) {
                if (usedv[i] == j) continue;
                if (!used[j] && min_ > g[usedv[i]][j]) {
                    min_ = g[usedv[i]][j];
                    v = j;
                }
            }
        }

        ret += min_;
        usedv.push_back(v);
        used[v] = true;
    }

    return ret;
}

int n, g[MAX_V + 1][MAX_V + 1];

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    cin >> n;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            cin >> g[i][j];
            if (g[i][j] == -1) g[i][j] = INF;
        }
    }

    cout << Prim(g, n, 0) << endl;


    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
static const int MAX=100;
static const int INF=(1<<21);
static const int WHI=0;
static const int GRA=1;
static const int BLA=2;
int n,M[MAX][MAX];
int prim(){
  int u,minv;
  int d[MAX],p[MAX],color[MAX];
  for(int i=0;i<n;i++){
    d[i]=INF;
    p[i]=-1;
    color[i]=WHI;
  }
  d[0]=0;
  while(1){
    minv=INF;
    u=-1;
    for(int i=0;i<n;i++){
      if(minv>d[i]&&color[i]!=BLA){
	u=i;
	minv=d[i];
      }
    }
    if(u==-1) break;
    color[u]=BLA; //ここで訪問に記録
    for(int v=0;v<n;v++){
      if(color[v]!=BLA&&M[u][v]!=INF){
	if(M[u][v]<d[v]){
	  d[v]=M[u][v];
	  p[v]=u;
	  color[v]=GRA;
	}
      }
    }
  }
  int sum=0;
  for(int i=0;i<n;i++){
    if(p[i]!=-1) sum+=M[i][p[i]];
  }
  return sum;
}
int main(){
  cin>>n;
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      int e;
      cin>>e;
      if(e==-1){
	M[i][j]=INF;
      }else{
	M[i][j]=e;
      }
    }
  }
  cout<<prim()<<endl;
  return(0);
}

C++: #include <bits/stdc++.h>
using namespace std;
#define N 100
int G[N][N];
int n;

int prim()
{
    int visited[n];
    int d[n];
    int p[n];

    for (int i; i < n; i++)
    {
        visited[i] = 0;
        d[i] = 114514;
    }

    d[0] = 0;
    p[0] = -1;

    while (true)
    {
        int mincost = 114514;
        int u;
        for (int i = 0; i < n; i++)
        {
            if (!visited[i] && d[i] < mincost)
            {
                mincost = d[i];
                u = i;
            }
        }

        if (mincost == 114514)
            break;

        visited[u] = 1;

        for (int i = 0; i < n; i++)
        {
            if (!visited[i] && G[u][i] != -1)
            {
                if (G[u][i] < d[i])
                {
                    d[i] = G[u][i];
                    p[i] = u;
                }
            }
        }
    }

    int sum = 0;
    for (int i = 1; i < n; i++)
        sum += d[i];
    return sum;
}

int main()
{
    cin >> n;
    int a;
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            cin >> a;
            if (a == -1)
                G[i][j] = 114514;
            else
                G[i][j] = a;
        }
    }
    cout << prim() << endl;
}

C++: //include
//------------------------------------------
#include <iostream>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <limits>
using namespace std;

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define FORR(i,a,b) for(int i=(a);i>(b);i--)
#define REP(i,n)  FOR(i,0,n)

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//debug
//-------------------------------------------
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#define INF std::numeric_limits<int>::max()

//typedef
//-------------------------------------------
typedef long long ll;

int n;
int g[101][101];

int prim(int used, int sum) {
    if (used == 0) return sum;

    int tmp = INF;
    int use = -1;
    REP(i, n) {
        if ((used>>i)&1) {
            continue;
        }
        REP(j, n) {
            if (((used>>j)&1) && g[i][j] < tmp) {
                tmp = g[i][j];
                use = j;
            }
        }
    }
    return prim(used&(~(1<<use)), sum + tmp);
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    cin >> n;
    REP(i, n) REP(j, n) {
        cin >> g[i][j];
        if (g[i][j] < 0) g[i][j] = INF;
    }
    int used = (1<<n) - 1;
    cout << prim(used&(~1), 0) << endl;

    return 0;
}