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"

#define REP(i,num) for(int i=0;i<(num);++i)
#define ALL(c) c.begin(),c.end()
#define PRINTALL(c) for(auto& x:c){cout<<x<<' ';}cout<<endl;
#define PAIRCOMP(c,comp) [](const pair<ll,ll>& lhs,const pair<ll,ll>& rhs){return lhs.c comp rhs.c;}

using namespace std;
using ll = long long;

constexpr ll atcoder_mod = 1e9+7;

template<typename T=int>
T in(){T x; cin >> x; return (x);}
template<typename T=int,typename C=vector<T>>
C vecin(int N){C x(N);REP(i,N){x[i]=in<T>();}return move(x);}

void vout(){cout << endl;}
template<typename Head,typename... Tail>
void vout(Head&& h,Tail&&... t){cout << ' ' << h;vout(forward<Tail>(t)...);}
void out(){cout << endl;}
template<typename Head,typename... Tail>
void out(Head&& h,Tail&&... t){cout << h;vout(forward<Tail>(t)...);}

class Edge{
public:
	ll to,weight;
	bool use{true};
	Edge(ll t,ll w):to(t),weight(w){}
};

class Edge2{
public:
	ll from,to,weight;
	Edge2()=default;
	Edge2(ll f,ll t,ll w):from(f),to(t),weight(w){}
};

class ConnectNodeInfo{
	vector<vector<Edge>> graph;
public:
	ConnectNodeInfo(int node_num){
		graph.resize(node_num);
	}
	void AddNonDirectionalConnection(ll u,ll v,ll w){
		graph[u].emplace_back(v,w);
		graph[v].emplace_back(u,w);
	}
	void AddDirectionalConnection(ll u,ll v,ll w){
		graph[u].emplace_back(v,w);
	}
	vector<Edge>& operator[](ll index){
		return graph[index];
	}
	size_t size(){return graph.size();}
};

class SearchPath{
	set<ll> visit;

	bool CanReachImpl(int start,int end,ConnectNodeInfo& connect){
		bool reach=false;
		if(start==end) return true;

		for(int i=0,ei=connect[start].size();i<ei;i++){
			if(!connect[start][i].use) continue;
			auto res = visit.emplace(connect[start][i].to);
			if(!res.second) continue;
			reach |= CanReachImpl(connect[start][i].to,end,connect);
		}
		return reach;
	}
public:
	bool CanReach(int start,int end,ConnectNodeInfo& connect){
		visit.clear();
		visit.emplace(start);
		return CanReachImpl(start,end,connect);
	}
};

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

	int N=in();
	vector<vector<int>> C(N,vector<int>(N));
	ConnectNodeInfo connect(N);
	vector<Edge2> edge;
	REP(i,N){
		REP(j,N){
			C[i][j]=in();
		}
	}
	REP(i,N){
		for(int j=i;j<N;j++){
			int v=C[i][j];
			if(v!=-1){
				connect.AddNonDirectionalConnection(i,j,v);
				edge.emplace_back(i,j,v);
			}
		}
	}
	sort(ALL(edge),[](Edge2& l,Edge2& r){return l.weight>r.weight;});
	SearchPath sp;
	int M=edge.size();
	ll sum=0;
	REP(i,M){
		auto& e=edge[i];
		for(auto& x:connect[e.from]){
			if(x.to==e.to) x.use=false;
		}
		for(auto& x:connect[e.to]){
			if(x.to==e.from) x.use=false;
		}
		if(!sp.CanReach(e.from,e.to,connect)){
			for(auto& x:connect[e.from]){
				if(x.to==e.to) x.use=true;
			}
			for(auto& x:connect[e.to]){
				if(x.to==e.from) x.use=true;
			}
			sum+=e.weight;
		}
	}
	
	out(sum);
	return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstdlib>
#include <string>
#include <iostream>
#include <climits>
#include <list>
#include <queue>

using namespace std;

static const int INFTY = 2001;

int H;
int A[101];
int NodeNum[101];
int IndexInA[100];


int parent(int i) {
	return i / 2;
}

int left(int i) {
	return 2 * i;
}

int right(int i) {
	return 2 * i + 1;
}

void minHeapify(int i) {
	int l = left(i);
	int r = right(i);
	int smallest = i;
	if (l <= H && A[l] < A[i]) {
		smallest = l;
	}
	if (r <= H && A[r] < A[smallest]) {
		smallest = r;
	}
	if (smallest != i) {
		int temp = A[i];
		A[i] = A[smallest];
		A[smallest] = temp;
		temp = NodeNum[i];
		NodeNum[i] = NodeNum[smallest];
		NodeNum[smallest] = temp;
		IndexInA[NodeNum[i]] = i;
		IndexInA[NodeNum[smallest]] = smallest;

		minHeapify(smallest);
	}
}

void insert(int d, int nodeNum) {
	int i = ++H;
	A[i] = d;
	NodeNum[i] = nodeNum;
	IndexInA[nodeNum] = i;
	int p = parent(i);
	while (i > 1 && A[p] > A[i]) {
		int temp = A[p];
		A[p] = A[i];
		A[i] = temp;
		temp = NodeNum[p];
		NodeNum[p] = NodeNum[i];
		NodeNum[i] = temp;
		IndexInA[NodeNum[p]] = p;
		IndexInA[NodeNum[i]] = i;
		i = p;
		p = parent(i);
	}
}

int heapExtractMinNodeNum() {
	int minNodeNum = NodeNum[1];
	A[1] = A[H];
	NodeNum[1] = NodeNum[H];
	IndexInA[NodeNum[1]] = 1;
	H--;
	minHeapify(1);

	return minNodeNum;
}

void decrese(int i, int value) {
	A[i] = value;
	int p = parent(i);
	while (i > 1 && A[p] > A[i]) {
		int temp = A[p];
		A[p] = A[i];
		A[i] = temp;
		temp = NodeNum[p];
		NodeNum[p] = NodeNum[i];
		NodeNum[i] = temp;
		IndexInA[NodeNum[p]] = p;
		IndexInA[NodeNum[i]] = i;
		i = p;
		p = parent(i);
	}
}

int main() {
	int Dist[101];
	int AdjacenceyList[100][100];
	int AdjacenceyWeightList[100][100];
	int Degree[100];
	int i, j;
	int N;
	int W;
	int Deg;
	int MinTotalWeight = 0;
	int u, v;
	bool inT[100];

	cin >> N;

	for (i = 0; i < N; i++) {
		inT[i] = false;
		Dist[i] = INFTY;
		Deg = -1;
		for (j = 0; j < N; j++) {
			cin >> W;
			if(W != -1){
				AdjacenceyList[i][++Deg] = j;
				AdjacenceyWeightList[i][Deg] = W;
			}
		}
		Degree[i] = Deg + 1;
	}
	Dist[100] = INFTY;



	H = 0;
	u = 0;
	inT[u] = true;
	Dist[u] = 0;
	for (i = 1; i <= N - 1; i++) {
		for (j = 0; j < Degree[u]; j++) {
			v = AdjacenceyList[u][j];
			if (inT[v] == false) {
				W = AdjacenceyWeightList[u][j];
				if (Dist[v] == INFTY) {
					Dist[v] = W;
					insert(W, v);
				}
				else if (W < Dist[v]) {
					Dist[v] = W;
					decrese(IndexInA[v], W);
				}
			}
		}

		int minNodeNum = heapExtractMinNodeNum();
		inT[minNodeNum] = true;
		MinTotalWeight += Dist[minNodeNum];
		u = minNodeNum;

		////DEBUG
		////printf("%d\n", minNodeNum);
		//for (int k = 1; k <= H; k++) {
		//	printf("(%d, %d) ", A[k], NodeNum[k]);
		//}
		//printf("\n");
	}

	printf("%d\n", MinTotalWeight);

	return 0;
}