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>
#define N 100
#define INF 1000000
using namespace std;

int main(){
  int n,g[N][N],used[N]={},d[N]={},p[N];
  cin>>n;
  for(int i=0;i<n;i++){
    d[i]=INF,p[i]=-1;
    for(int j=0;j<n;j++){
      cin>>g[i][j];
      if(g[i][j]==-1) g[i][j]=INF;
    }
  }
  d[0]=0;
  
  while(1){
    int j=-1,min=INF;
    for(int i=0;i<n;i++)if(!used[i] && d[i]<min)min=d[i],j=i;
    if(j==-1) break;
    used[j]=1;
    for(int k=0;k<n;k++)
      if(!used[k] && g[j][k]!=INF)if(g[j][k]<d[k])d[k]=g[j][k],p[k]=j;
  }
int ans=0;
for(int i=0;i<n;i++)if(p[i]!=-1)ans+=g[i][p[i]];
cout<<ans<<endl;
 
 return 0;
}

C++: #include <algorithm>
#include <bitset>
#include <cassert>
#include <complex>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <typeinfo>
#include <utility>
#include <vector>
#include <array>
#include <chrono>
#include <random>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, ...)type __VA_ARGS__;Scan(__VA_ARGS__);
template<typename T> void Scan(T& t) { std::cin >> t; }
template<typename First, typename...Rest>void Scan(First& first, Rest&...rest) { std::cin >> first; Scan(rest...); }
#define OUT(d) std::cout<<d;
#define FOUT(n, d) std::cout<<std::fixed<<std::setprecision(n)<<d;
#define SOUT(n, c, d) std::cout<<std::setw(n)<<std::setfill(c)<<d;
#define SP std::cout<<" ";
#define TAB std::cout<<"\t";
#define BR std::cout<<"\n";
#define FLUSH std::cout<<std::flush;
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& r:c)for(auto& i:r)std::cin>>i;
#define ALL(a) (a).begin(),(a).end()
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define RFOR(i, a, b) for(int i=(b)-1;i>=(a);--i)
#define REP(i, n) for(int i=0;i<int(n);++i)
#define RREP(i, n) for(int i=(n)-1;i>=0;--i)
#define FORLL(i, a, b) for(ll i=ll(a);i<ll(b);++i)
#define RFORLL(i, a, b) for(ll i=ll(b)-1;i>=ll(a);--i)
#define REPLL(i, n) for(ll i=0;i<ll(n);++i)
#define RREPLL(i, n) for(ll i=ll(n)-1;i>=0;--i)
#define PAIR std::pair<int, int>
#define IN(a, x, b) (a<=x && x<b)
#define SHOW(d) {std::cout << #d << "\t:" << d << "\t";}
#define SHOWVECTOR(v) {std::cout << #v << "\t:";for(const auto& i : v){std::cout << i << " ";}std::cout << "\n";}
#define SHOWVECTOR2(v) {std::cout << #v << "\t:\n";for(const auto& i : v){for(const auto& j : i){std::cout << j << " ";}std::cout << "\n";}}
#define SHOWPAIRVECTOR2(v) {std::cout << #v << "\t:\n";for(const auto& i : v){for(const auto& j : i){std::cout<<'('<<j.first<<", "<<j.second<<") ";}std::cout << "\n";}}
#define SHOWPAIRVECTOR(v) {for(const auto& i:v){std::cout<<'('<<i.first<<", "<<i.second<<") ";}std::cout<<"\n";}
#define CHECKTIME(state) {auto start=std::chrono::system_clock::now();state();auto end=std::chrono::system_clock::now();auto res=std::chrono::duration_cast<std::chrono::nanoseconds>(end-start).count();std::cerr<<"[Time:"<<res<<"ns  ("<<res/(1.0e9)<<"s)]\n";}
#define SHOWQUEUE(a) {std::queue<decltype(a.front())> tmp(a);std::cout << #a << "\t:";for(int i=0; i<static_cast<int>(a.size()); ++i){std::cout << tmp.front() << "\n";tmp.pop();}std::cout << "\n";}

//#define int ll
using ll = long long;
using ull = unsigned long long;
constexpr int INFINT = 1 << 30;
constexpr ll INFLL = 1LL << 60;
constexpr double EPS = 0.0000000001;
constexpr int MOD = 1000000007;

//Union-Find
class UnionFind {
private:
	std::vector<int> parent;
	std::vector<int> height;

public:
	UnionFind(int size) : parent(size), height(size, 0) {
		REP(i, size) {
			parent[i] = i;
		}
	}
	void init(int size) {
		parent.resize(size);
		height.resize(size, 0);
		REP(i, size) {
			parent[i] = i;
		}
	}
	int find(int x) {
		if (parent[x] == x) {
			return x;
		}
		return parent[x] = find(parent[x]);
	}
	void unite(int x, int y) {
		x = find(x);
		y = find(y);
		if (x == y) return;
		if (height[x] < height[y]) parent[x] = y;
		else parent[y] = x;
		if (height[x] == height[y]) ++height[x];
	}
	bool same(int x, int y) {
		return find(x) == find(y);
	}
};

struct Edge {
	int from, to, cost;
	Edge(int f, int t, int c) : from(f), to(t), cost(c) {};
};
bool operator<(const Edge& l, const Edge& r) {
	return l.cost < r.cost;
}

signed main() {
	INIT;
	VAR(int, n);
	MAT(int, a, n, n);
	UnionFind uf(n);
	std::priority_queue<Edge> pq;
	REP(i, n) FOR(j, i + 1, n) {
		if (a[i][j] != -1) {
			pq.push(Edge(i, j, -a[i][j]));
		}
	}
	int ans = 0;
	while (!pq.empty()) {
		Edge now = pq.top(); pq.pop();
		if (uf.same(now.from, now.to)) continue;
		uf.unite(now.from, now.to);
		ans -= now.cost;
	}
	OUT(ans)BR;
	return 0;
}