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>
#include <cmath>

using namespace std;
typedef long long ll;
//typedef unsigned long long ll;

#define rep(i, n) for (int i = 0; i < (n); ++i)
//#define rep(i, n) for (ll i = 0; i < (n); ++i)
//#define sz(x) ll(x.size())
//typedef pair<ll, int> P;
//typedef pair<ll, ll> P;
const double INF = 1e10;
//const ll INF = LONG_LONG_MAX / 10;
//const ll INF = 1e15;
const ll MINF = LONG_LONG_MIN;
//const int INF = INT_MAX / 10;
#define cmin(x, y) x = min(x, y)
#define cmax(x, y) x = max(x, y)

bool contain(set<int> &s, int a) { return s.find(a) != s.end(); }

//ifstream myfile("C:\\Users\\riku\\Downloads\\0_00.txt");
//ofstream outfile("log.txt");
//outfile << setw(6) << setfill('0') << prefecture << setw(6) << setfill('0') << rank << endl;
// std::cout << std::bitset<8>(9);

typedef pair<double, double> P;

void print_line(vector<int> &line) {
    if (line.size() == 0ll) {
        cout << endl;
        return;
    }
    for (ll i = 0; i < line.size(); i++) {
        cout << line[i];
        if (i == line.size() - 1) cout << endl;
        else cout << ' ';
    }
}


typedef priority_queue<long long, vector<long long>, greater<long long>> PQ_ASK;
const int mod = 1000000007;

class UnionFind {
public:
    // 親の番号を格納する。親だった場合-size
    vector<int> parents;

    UnionFind(int n) {
        parents = vector<int>(n, -1);
    }

    // aがどのグループに属しているか
    int root(int a) {
        if (parents[a] < 0) {
            return a;
        }
        return parents[a] = root(parents[a]);
    }

    int size(int a) {
        return -parents[root(a)];
    }

    // aとbをくっつける
    bool connect(int a, int b) {
        int ra = root(a);
        int rb = root(b);
        if (ra == rb) {
            return false;
        }
        // 大きいほうにA
        if (size(ra) < size(rb)) {
            swap(ra, rb);
        }
        parents[ra] += parents[rb];
        parents[rb] = ra;
        return true;
    }

};

struct Road {
    int from, to, cost;
};

int main() {
    int n;
    cin >> n;

    vector<Road> road;

    rep(i, n) rep(j, n) {
            int cost;
            cin >> cost;
            if (cost == -1) continue;
            road.push_back({i, j, cost});
        }

    sort(road.begin(), road.end(), [](Road &r, Road &s) { return r.cost < s.cost; });

    UnionFind uf(n);
    ll cost = 0;
    for (Road &r : road) {
        if (uf.root(r.from) == uf.root(r.to)) continue;
        uf.connect(r.from, r.to);
        cost += r.cost;
    }
    cout << cost << endl;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using vi = vector<int>;    using vvi = vector<vi>;
using vb = vector<bool>;   using vvb = vector<vb>;
using vl = vector<ll>;     using vvl = vector<vl>;
using vd = vector<double>; using vvd = vector<vd>;

#define REP(i,n) for(auto i = 0 * n; i < (n); ++i)
#define ALL(c) (c).begin(), (c).end()
#define FOR(i,s,e) for (ll i = s; i < (ll)e; i++)
#define TEN(x) ((ll)1e##x)


struct Edge{ uint32_t to, id; };
typedef vector<vector<Edge>> Graph;

template<class T> struct Prim {
	Prim(const Graph & es, const vector<T> & ws) : g(es.size()) {
		typedef uint32_t U;
		typedef tuple<T, U, U, U> P;
		U n = es.size();
		vector<U> unexp(n, 1);
		priority_queue<P, vector<P>, greater<P>> q; q.emplace(0, n, 0, 0);
		while (!q.empty()) {
			T w; U u, v, i; tie(w, u, v, i) = q.top(); q.pop();
			if (unexp[v]) {
				unexp[v] = 0;
				if (u != n) { g[u].push_back({ v, i }); g[v].push_back({ u, i }); cost += w; }
				for (auto e : es[v]) if (unexp[e.to]) q.emplace(ws[e.id], v, e.to, e.id);
			}
		}
	}
	Graph g; T cost = 0;
};

int main() {
	cin.tie(0);
	ios_base::sync_with_stdio(false);
	cout << fixed << setprecision(50);

	size_t n; cin >> n;
	Graph g(n);
	vl w;
	REP(i, n) REP(j, n) {
		ll x; cin >> x;
		if (x != -1) {
			g[i].push_back(Edge{j, w.size()});
			g[j].push_back(Edge{i, w.size()});
			w.push_back(x);
		}
	}
	Prim<ll> mst(g, w);
	cout << mst.cost << endl;
}