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<string>
#include<cstdlib>
#include<map>
#include<iomanip>
#include<sstream>
#include<vector>
#include<stack>
#include<math.h>
#include<queue>
#include<complex>
#include<random>
#include<ctime>
using namespace std;
long long int INF=99999999999999;

//INFを宣言すること。Edgeに辺の情報を入れよう。
class Graph{
//メンバ変数の説明
//Edge:一つ目の番号が辺が出る方向
//MaxV,MaxE:頂点数と辺の数
//Result系:各メソッドの答え
//InfinteUpdate:BellmanFordで各番号の頂点までの最短経路が更新されるか
//
public:
	vector<pair<long long int,long long int> > *Edge;
	vector<pair<pair<long long int,long long int>,long long int > >PrimEdge;
	long long int MaxV,MaxE;
	long long int *BellmanFordResult,*DijkstraResult,**WarshallFloydResult;
	bool *InfiniteUpdate;
	bool NegativeLoop=false;
	long long int PrimResult=0;
	bool NotConected=false;


	Graph(long long int InputV,long long int InputE){
		MaxV=InputV;
		MaxE=InputE;
		Edge=new vector<pair<long long int,long long int> >[InputV+1];

	}
	
	void BellmanFord(long long int Start) {
		BellmanFordResult=new long long int[MaxV];
		InfiniteUpdate=new bool[MaxV];
		for (int i = 0; i < MaxV; i++) { BellmanFordResult[i] = INF;InfiniteUpdate[i]=false; }
		BellmanFordResult[Start] = 0;
		long long int turn=0;
		while (true) {
			turn++;
			bool update = false;
			for (int i = 0; i < MaxV; i++) {
				for(int j=0;j<Edge[i].size();j++){
					pair<long long int,long long int> e = Edge[i][j];
					if(turn>=MaxV&&InfiniteUpdate[i])
					{
						InfiniteUpdate[e.first]=true;
					}
					if (BellmanFordResult[i] != INF && BellmanFordResult[e.first] > BellmanFordResult[i] + e.second) {
						BellmanFordResult[e.first] = BellmanFordResult[i] + e.second;
						update = true;
						if(turn>=MaxV){
							InfiniteUpdate[e.first]=true;
						}
					}
				}
			}
			if (!update) { 
				NegativeLoop=false;
				break; 
			}
			if(turn>=2*MaxV-1){
				NegativeLoop=true;
				break;
			}
		}
	}

	void Dijkstra(long long int Start) {
		DijkstraResult=new long long int[MaxV];
		priority_queue<pair<long long int,long long int>, vector<pair<long long int,long long int> >, greater<pair<long long int,long long int> > >que;
		fill(DijkstraResult, DijkstraResult + MaxV, INF);
		DijkstraResult[Start] = 0;
		que.push(pair<long long int,long long int>(0, Start));

		while (!que.empty()) {
			pair<long long int,long long int> p = que.top();
			que.pop();
			long long int v = p.second;
			if (DijkstraResult[v] < p.first)continue;
			for (int i = 0; i < Edge[v].size(); i++) {
				pair<long long int,long long int> e = Edge[v][i];
				if (DijkstraResult[e.first] > DijkstraResult[v] + e.second) {
					DijkstraResult[e.first] = DijkstraResult[v] + e.second;
					que.push(pair<long long int,long long int>(DijkstraResult[e.first], e.first));
				}
			}
		}
	}

	void WarshallFloyd() {
		WarshallFloydResult=new long long int*[MaxV];
		for(int i=0;i<MaxV;i++){
			WarshallFloydResult[i]=new long long int[MaxV];
		}
		for(int i=0;i<MaxV;i++){
			for(int j=0;j<Edge[i].size();j++){
				WarshallFloydResult[i][Edge[i][j].first]=Edge[i][j].second;
			}
		}

		for (int k = 0; k < MaxV; k++) {
			for (int i = 0; i < MaxV; i++) {
				for (int j = 0; j < MaxV; j++) {
					WarshallFloydResult[i][j] = min(WarshallFloydResult[i][j], WarshallFloydResult[i][k] + WarshallFloydResult[k][j]);
				}
			}
		}
	}
	
	 void Prim(){
	 	NotConected=false;
	 	priority_queue<pair<long long int,pair<long long int,long long int> >,vector<pair<long long int,pair<long long int,long long int> > > ,greater<pair<long long int,pair<long long int,long long int> > > >PriorityEdge;
	 	bool *IncludedVertex=new bool[MaxV];
	 	fill(IncludedVertex,IncludedVertex+MaxV,false);
	 	PrimEdge.clear();
	 	for(int i=0;i<Edge[0].size();i++)
	 	{
	 		PriorityEdge.push({Edge[0][i].second,{0,Edge[0][i].first}});
	 	}
	 	IncludedVertex[0]=true;
	 	for(int i=0;i<MaxV-1;i++)
	 	{
	 		while(1)
	 		{
	 			if(PriorityEdge.empty())
	 			{
	 				NotConected=true;
	 				break;
	 			}
	 			pair<long long int,pair<long long int,long long int> > pe = PriorityEdge.top();
	 			PriorityEdge.pop();
	 			//cout<<pe.first<<" "<<pe.second.first<<" "<<pe.second.second<<endl;
	 			if(!IncludedVertex[pe.second.second])
	 			{
	 				IncludedVertex[pe.second.second]=true;
	 				PrimResult+=pe.first;
	 				PrimEdge.push_back({pe.second,pe.first});
	 				//cout<<"size"<<pe.second.second<<" "<<Edge[pe.second.second].size()<<endl;
	 				for(int j=0;j<Edge[pe.second.second].size();j++)
	 				{
	 					PriorityEdge.push({Edge[pe.second.second][j].second,{pe.second.second,Edge[pe.second.second][j].first}});
	 				}
	 				break;
	 			}
	 			
	 			
	 		}
	 	}
	 }
};

int main(){
	
	long long int N,M=0,P,a[101][101];
	cin>>N;
	for(int i=0;i<N;i++)
	{
		for(int j=0;j<N;j++)
		{
			cin>>a[i][j];
			if(a[i][j]!=-1)
			{
				M++;
			}
		}	
	}
	
	Graph graph(N,M);
	for(int i=0;i<N;i++)
	{
		for(int j=0;j<N;j++)
		{
			if(a[i][j]!=-1)
			{
				graph.Edge[i].push_back({j,a[i][j]});
			}
		}	
	}
	graph.Prim();
	cout<<graph.PrimResult<<endl;
	
}