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 <iostream>
#include <queue>

using namespace std;

using pii = pair<int, int>;

struct Graph{
  int v_size;
  vector<vector<pii>> adj;
  
  Graph(const int v_size):v_size(v_size){
    this->adj.resize(v_size);
  }
  
  void add_edge(const int s, const int t, const int w){
    this->adj[s].emplace_back(pii(t, w));
  }
};

int mst(const Graph& g){
  constexpr int INF{INT_MAX};
  
  vector<int> d(g.v_size, INF);
  priority_queue<pii, vector<pii>, greater<pii>> pq;

  d[0] = 0;
  pq.push(pii(0, 0));

  int ans {0};
  
  while(!pq.empty()){
    auto cost {pq.top().first};
    auto v {pq.top().second};
    pq.pop();

    if(d[v] < cost) continue;

    ans += cost;
    d[v] = -INF;

    for(int i = 0; i < g.adj[v].size(); ++i){
      auto to {g.adj[v][i].first};
      auto next_cost {g.adj[v][i].second};

      if(d[to] > next_cost){
        d[to] = next_cost;
        pq.push(pii(next_cost, to));
      }
    }
  }

  return ans;
}

int main()
{
  int n;
  cin >> n;
  
  Graph g(n);

  int x;
  for(int i = 0; i < n; ++i){
    for(int j = 0; j < n; ++j){
      cin >> x;
      if(x != -1){
        g.add_edge(i, j, x);
      }
    }
  }

  cout << mst(g) << endl;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define INF 1000000000

int m[100][100],n;

int prim(){
  int u,minv;
  int d[100],p[100],c[100];
  for(int i=0;i<n;i++){
    d[i]=INF;
    p[i]=-1;
    c[i]=0;
  }
  d[0]=0;
  while(1){
    minv=INF;
    u=-1;
    for(int i=0;i<n;i++){
      if(minv>d[i] && c[i]!=2){
	u=i;
	minv=d[i];
      }
    }
    if(u==-1) break;
    c[u]=2;
    for(int i=0;i<n;i++){
      if(c[i]!=2 && m[u][i]!=INF){
	if(d[i]>m[u][i]){
	  d[i]=m[u][i];
	  p[i]=u;
	  c[i]=1;
	}
      }
    }
  }
  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;
      m[i][j]=(e==-1)?INF:e;
    }
  }
  cout<<prim()<<endl;
  return 0;
}

C++: #include <cassert>

#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
// #include <boost/foreach.hpp>
// #include <boost/range/algorithm.hpp>
#define rep(i,j,k) for(int i=(int)j;i<(int)k;i++)
#define ll long long
#define Sort(v) sort(all(v))
//#define INF 1e9
#define LINF 1e18
#define END return 0
#define pb push_back
#define se second
#define fi first
#define pb push_back
#define all(v) (v).begin() , (v).end()
#define MP make_pair
#define int long long
using namespace std;
int day[12]={31,28,31,30,31,30,31,31,30,31,30,31};
// int dx[]={0,1,0,-1};
// int dy[]={1,0,-1,0};
struct edge{int to,cost;};
//typedef pair<int,int> P;

const long long MOD=1000000007LL;
bool isupper(char c){if('A'<=c&&c<='Z')return 1;return 0;}
bool islower(char c){if('a'<=c&&c<='z')return 1;return 0;}
bool isPrime(int x){if(x==1)return 0;if(x==2)return 1;if(x%2==0)return 0;for(int i=3;i*i<=x;i++)if(x%i==0)return 0;return 1;}
bool iskaibun(string s){for(int i=0;i<s.size()/2;i++)if(s[i]!=s[s.size()-i-1])return 0;return 1;}
bool isnumber(char c){return ('0'<=c&&c<='9');}
bool isalpha(char c){return (isupper(c)||islower(c));}
template<typename T> 
void print(vector<T> v){
    for(int i=0;i<v.size();i++){
        if(i)cout<<" ";
        cout<<v[i];
    }
    cout<<endl;
}
int INF=1e18;

template<typename T>
void printendl(vector<T> v){
    for(auto date:v)cout<<date<<endl;
}

template<typename T>
void printvv(vector<vector<T>> v){
    for(int i=0;i<v.size();i++){
        for(int j=0;j<v[i].size();j++){
            if(j)cout<<" ";
            cout<<v[i][j];
        }
        cout<<endl;
    }
}
int gcd(int a,int b){
    if(a<b)swap(a,b);
    if(b==0)return a;
    else return gcd(b,a%b);
}

struct Edge{
    int to,cost;
};

int prim(vector<vector<Edge>>& g, int n){
    typedef pair<int,int> P;
    vector<bool> used(n+1,false);
    int ret=0;
    priority_queue<P, vector<P>, greater<P>> que;
    que.push(P(0, 0)); //(コスト, 頂点)
    while(!que.empty()){
        P p=que.top();
        que.pop();
        if(used[p.second])continue;
        used[p.second]=true;
        ret+=p.first;
        for(int i=0;i<g[p.second].size();i++){
            Edge e=g[p.second][i];
            que.push(P(e.cost, e.to));
        }
    }
    return ret;
}

signed main (){
    int n;
    cin>>n;
    vector<vector<Edge>> v(n,vector<Edge>(0));
    rep(i,0,n){
        rep(j,0,n){
            int x;
            cin>>x;
            if(x!=-1){
                v[i].push_back(Edge{j,x});
            }
        }
    }
    cout<<prim(v,n)<<endl;

}
/*

*/