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++: #define _CRT_SECURE_NO_WARNINGS
// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
template<class T> ostream &operator << (ostream &os, const vector<T> &);
template<size_t n, class...T> typename enable_if<(n>=sizeof...(T))>::type _ot(ostream &, const tuple<T...> &){}
template<size_t n, class...T> typename enable_if<(n< sizeof...(T))>::type _ot(ostream &os, const tuple<T...> &t){
    os << (n == 0 ? "" : " ") << get<n>(t); _ot<n+1>(os, t);
}
template<class...T> ostream &operator << (ostream &os, const tuple<T...> &t){
    _ot<0>(os, t); return os;
}
template<class T, class U> ostream & operator << (ostream &os, const pair<T,U> &p){
    return os << "(" << p.first << ", " << p.second << ") ";
}
template<class T> ostream &operator << (ostream &os, const vector<T> &v){
    for(size_t i = 0; i < v.size(); i++) os << v[i] << (i + 1 == v.size() ? "" : ", "); return os;
}
#ifdef DEBUG
#define dump(...) (cerr << #__VA_ARGS__ << " = " << make_tuple(__VA_ARGS__) \
                   << " (L : " << __LINE__ << ")" << endl)
#else
#define dump(...)
#endif
#define all(c) begin(c), end(c)
#define range(i,a,b) for(int i = a; i < (int)(b); i++)
#define rep(i,b) range(i,0,b)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
typedef long long ll;
// #define int ll
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
void fastios(){ ios_base::sync_with_stdio(0); cin.tie(0); }
int const mod = 1000000007;
auto const inf = numeric_limits<int>::max()/8;

using Weight = int;
using Capacity = int;
struct Edge {
    int src, dst; Weight weight;
    Edge(int s, int d, int w) : src(s), dst(d), weight(w) {}
};
using Edges = vector<Edge>;
using Graph = vector<Edges>;
using Array = vector<Weight>;
using Matrix = vector<Array>;

struct UnionFind {
    vector<int> par;
    int cnt;
    UnionFind(int size_) : par(size_, -1), cnt(size_) { }
    bool merge(int x, int y){
        x = find(x); y = find(y);
        if (x != y) {
            if (par[y] < par[x]) swap(x, y);
            par[x] += par[y]; par[y] = x; cnt--;
        }
        return x != y;
    }
    bool get(int x, int y){ return find(x) == find(y); }
    int find(int x){ return par[x] < 0 ? x : par[x] = find(par[x]); }
    int size(int x){ return -par[find(x)]; }
    int size(){ return cnt; }
};

bool operator < (const Edge &e, const Edge &f){ return e.weight > f.weight; }
pair<Weight, Edges> kruskal(Graph const& g){
    UnionFind uf(g.size());
    Edges es; rep(i, g.size()) for(auto &e : g[i]) es.emplace_back(e);
    sort(all(es)); reverse(all(es)); // !! INVERSE !!
    Weight total = 0; Edges T;
    for(auto &e : es){
        if(uf.get(e.src,e.dst)) continue;
        T.push_back(e); total += e.weight; uf.merge(e.src,e.dst);
    }
    return make_pair(total, T);
}

int main(){
    int n;
    cin >> n;
    Graph g(n);
    for(int i = 0; i < n; i++){
        for(int j = 0; j < n; j++){
            int x;
            cin >> x;
            if(x != -1) g[i].emplace_back(i,j,x);
        }
    }
    cout << kruskal(g).first << endl;
}

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 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;
	int PrevSecondSmallestVertex;
	int SecondSmallestVertex;
	int MinVertex;
	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;

	u = 0;
	inT[u] = true;
	Dist[u] = 0;
	PrevSecondSmallestVertex = 100;
	for (i = 1; i <= N - 1; i++) {
		MinVertex = 100;
		for (j = 0; j < Degree[u]; j++) {
			v = AdjacenceyList[u][j];
			if (inT[v] == false) {
				W = AdjacenceyWeightList[u][j];
				if (W < Dist[v]) {
					Dist[v] = W;
				}
				if (Dist[v] < Dist[MinVertex]) {
					SecondSmallestVertex = MinVertex;
					MinVertex = v;
				}
				else if (Dist[v] < Dist[SecondSmallestVertex]) {
					SecondSmallestVertex = v;
				}
			}
		}

		////DEBUG
		//cout << "MinVerTex = " << MinVertex << " SecondSmallestVertex = " << SecondSmallestVertex << endl;

		if (Dist[PrevSecondSmallestVertex] < Dist[MinVertex]) {
			SecondSmallestVertex = MinVertex;
			MinVertex = PrevSecondSmallestVertex;
			PrevSecondSmallestVertex = SecondSmallestVertex;
		}
		else if (Dist[SecondSmallestVertex] < Dist[PrevSecondSmallestVertex]) {
			PrevSecondSmallestVertex = SecondSmallestVertex;
		}
		inT[MinVertex] = true;
		u = MinVertex;
		MinTotalWeight += Dist[MinVertex];

		////DEBUG
		//cout << "MinVertex = " << MinVertex << " PrevSecondSmallestVertex = " << PrevSecondSmallestVertex << endl;
		//cout << "inT: ";
		//for (int k = 0; k < N; k++) {
		//	cout << inT[k] << " ";
		//}
		//cout << endl;
		//printf("MinTotalWeight = %d\n", MinTotalWeight);
	}
	printf("%d\n", MinTotalWeight);

	return 0;
}