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 <bits/stdc++.h>
using namespace std;

typedef int64_t i64;
typedef uint64_t ui64;

class djset{
private:
    int sz;
    int *par;
public:
    djset(int n){
        sz=n;
        par=new int[sz];
        for(int i=0;i<sz;i++) par[i]=1;
    }
    int find(int x){
        return par[x]<=0?-(par[x]=-find(-par[x])):x;
    }
    void unite(int x,int y){
        int px=find(x),py=find(y);
        if(px==py) return;
        if(par[px]<par[py]){
            int tmp=px;
            px=py;
            py=tmp;
        }
        par[px]+=par[py];
        par[py]=-px;
    }
    bool same(int x,int y){
        return (find(x)==find(y));
    }
    int size(int x){
        return par[find(x)];
    }
    int group(void){
        int cnt=0;
        for(int i=0;i<sz;i++){
            if(par[i]>0) cnt++;
        }
        return cnt;
    }
    void refr(void){
        delete[] par;
    }
};

class graph{
private:
    struct vrtx{
        int to;
        int64_t cost;
    };
    struct adj{
        int start;
        int to;
        int64_t cost;
    };
    int nd;
    int edg;
public:
    std::vector<vrtx> *node;
    std::vector<adj> edge;
    graph(int n,int m){
        nd=n;
        edg=m;
        node=new std::vector<vrtx>[nd];
    }
    void add_dir(int s,int t,int64_t c){
        node[s].push_back({t,c});
        edge.push_back({s,t,c});
    }
    void add_undir(int s,int t,int64_t c){
        node[s].push_back({t,c});
        node[t].push_back({s,c});
        edge.push_back({s,t,c});
    }
    void dlt_dir(int s,int t){
        for(int i=0;i<node[s].size();i++){
            if(node[s][i].to==t){
                node[s].erase(node[s].begin()+i);
                break;
            }
        }
    }
    void dlt_undir(int s,int t){
        for(int i=0;i<node[s].size();i++){
            if(node[s][i].to==t){
                node[s].erase(node[s].begin()+i);
                break;
            }
        }
        for(int i=0;i<node[t].size();i++){
            if(node[t][i].to==s){
                node[t].erase(node[t].begin()+i);
                break;
            }
        }
    }
    void refr(void){
        for(int i=0;i<nd;i++) std::vector<vrtx>().swap(node[i]);
        delete[] node;
        std::vector<adj>().swap(edge);
    }
    bool islnk(void);
    void dfs(int r,int64_t **p,bool **vst);  // 木, (*p)[], vst[] を呼び出す前に初期化
    bool ispls(void);
    void bellford(int s,int64_t **d);
    void dijkstra(int s,int64_t **d);  // 負の閉路なし
    void bfs(int s,int64_t **d);  // 辺に重み無し or 木
    void waflo(bool isdir,int64_t ***d);
    int64_t minstw_dir(int r);  // class: djset, class: skewheap が必要
    int64_t minstw_undir(void);  // class: djset が必要
    void edmonds(int r,std::vector<std::pair<int,int>> &p);  // class: djset, class: skewheap が必要
    void kruscal(std::vector<std::pair<int,int>> &p);  // class: djset が必要
    void prim(std::vector<std::pair<int,int>> &p);
    void cumulsum(int s,int64_t **d);  // 木
    void cumulprd(int s,int64_t **d);  // 木
};

void graph::kruscal(std::vector<std::pair<int,int>> &p){
    adj *es=new adj[edg];
    for(int i=0;i<edg;i++) es[i]={edge[i].start,edge[i].to,edge[i].cost};
    std::sort(es,es+edg,[](const adj &e1,const adj &e2){return e1.cost<e2.cost;});
    djset uf(nd);
    for(int i=0;i<edg;i++){
        if(!uf.same(es[i].start,es[i].to)){
            uf.unite(es[i].start,es[i].to);
            p.push_back({es[i].start,es[i].to});
        }
    }
}

int64_t graph::minstw_undir(void){
    adj *es=new adj[edg];
    for(int i=0;i<edg;i++) es[i]={edge[i].start,edge[i].to,edge[i].cost};
    std::sort(es,es+edg,[](const adj &e1,const adj &e2){return e1.cost<e2.cost;});
    djset uf(nd);
    int64_t res=0;
    for(int i=0;i<edg;i++){
        if(!uf.same(es[i].start,es[i].to)){
            uf.unite(es[i].start,es[i].to);
            res+=es[i].cost;
        }
    }
    return res;
}

int main(void){
    int n;
    scanf("%i",&n);
    int m=0;
    i64 **d=new i64*[n];
    for(int i=0;i<n;i++){
        d[i]=new i64[n];
        for(int j=0;j<n;j++){
            scanf("%lli",&d[i][j]);
            if(d[i][j]!=-1) m++;
        }
    }
    graph g(n,m);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            if(d[i][j]!=-1) g.add_dir(i,j,d[i][j]);
        }
    }
    printf("%lli\n",g.minstw_undir());
    return 0;
}