Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
)

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

type ElementKey int
type Node struct {
	key    ElementKey
	parent *Node
	rank   int
}

func newNode(key ElementKey) *Node {
	node := Node{}
	node.key = key
	node.parent = &node
	node.rank = 0

	return &node
}

func union(x, y *Node) {
	xSet := findSet(x)
	ySet := findSet(y)
	link(xSet, ySet)
}

func link(x, y *Node) {
	if x.rank > y.rank {
		y.parent = x
	} else {
		x.parent = y

		if x.rank == y.rank {
			y.rank++
		}
	}
}

func findSet(x *Node) *Node {
	if x != x.parent {
		x.parent = findSet(x.parent)
	}
	return x.parent
}

func newDisjointSets(nSets int) *DisjointSets {
	sets := DisjointSets{}
	sets.keyToNode = map[ElementKey]*Node{}
	for i := 0; i < nSets; i++ {
		key := ElementKey(i)
		sets.keyToNode[key] = newNode(key)
	}
	return &sets
}

type DisjointSets struct {
	keyToNode map[ElementKey]*Node
}

func (sets *DisjointSets) union(x, y ElementKey) {
	xNode := sets.keyToNode[x]
	yNode := sets.keyToNode[y]
	union(xNode, yNode)
}

func (sets DisjointSets) findSet(x ElementKey) *Node {
	xNode := sets.keyToNode[x]
	return findSet(xNode)
}

type Edge struct {
	i, j   int
	weight int
}

func main() {
	scanner.Split(bufio.ScanWords)

	n := nextInt()
	sets := newDisjointSets(n)
	edges := []Edge{}
	a := make([][]int, n)
	for i := 0; i < n; i++ {
		a[i] = make([]int, n)
		for j := 0; j < n; j++ {
			a[i][j] = nextInt()
			if a[i][j] >= 0 {
				e := Edge{
					i:      i,
					j:      j,
					weight: a[i][j],
				}
				edges = append(edges, e)
			}
		}
	}
	sort.Slice(edges, func(i, j int) bool { return edges[i].weight < edges[j].weight })
	totalWeight := 0
	for _, edge := range edges {
		i := ElementKey(edge.i)
		j := ElementKey(edge.j)
		if sets.findSet(i) != sets.findSet(j) {
			totalWeight += edge.weight
			sets.union(i, j)
		}
	}
	fmt.Println(totalWeight)
}

Python: # -*- coding: utf-8 -*-

"""Minimum Spanning Tree"""

import sys
import os
import pprint

DEBUG = False

#fd = os.open('ALDS1_12_A.txt', os.O_RDONLY)
#os.dup2(fd, sys.stdin.fileno())

n = int(input())

# n x n matrix
M = []
for i in range(n):
    l = list(map(int, input().split()))
    M.append(l)

# Prim's Algorithm
INF = 1000000
visited = [False] * n
parent = [None] * n

# 0 is in T (Tree)
parent[0] = None

# distance between T and T-V
distance = [INF] * n
distance[0] = 0

while True:
    min_dist = INF
    candidate_index = None
    for i in range(n):
        if not visited[i] and distance[i] < min_dist:
            min_dist = distance[i]
            candidate_index = i

    if candidate_index is None:
        break

    if DEBUG:
        print('accepted i', candidate_index)
    visited[candidate_index] = True
    distance[candidate_index] = -1  # done

    for i in range(n):
        if not visited[i] and M[candidate_index][i] != -1 and distance[i] > M[candidate_index][i]:
            distance[i] = M[candidate_index][i]
            parent[i] = candidate_index


# Trees length
_sum = 0
for i in range(n):
    if parent[i] is not None:
        d = M[i][parent[i]]
        _sum += d
print(_sum)

Python: n=int(input())
matrix=[list(map(int,input().split())) for _ in range(n)]
weight=[]
for x in range(n):
    for y in range(x,n):
        if matrix[x][y]>=0: weight.append((x,y,matrix[x][y]))
weight.sort(key=lambda x:x[2])
ans=0
p=[i for i in range(n)]

def root(x):
    path_to_root=[]
    while p[x]!=x:
        path_to_root.append(x)
        x=p[x]
    for node in path_to_root:
        p[node]=x
    return x
    
def is_same_set(x,y):
    return root(x)==root(y)
    
def unite(x,y):
    p[root(x)]=root(y)
        
for x,y,w in weight:
    if not is_same_set(x,y):
        unite(x,y)
        ans+=w
print(ans)

Python: n = int(input())
edgeList = []
for i in range(n):
    a = list(map(int, input().split()))
    for j in range(i):
        if a[j] != -1:
            edgeList.append([a[j], getRoot(i), getRoot(j)])
rootList = [-1 for i in range(n)]
sumLength = 0

def getRoot(x):
    r = rootList[x]
    if r < 0:
        rootList[x] = x
    elif r != x:
        rootList[x] = getRoot(r)
    return rootList[x]
        

edgeList.sort(key=lambda x: x[0])
for e in edgeList:
    x = getRoot(e[1])
    y = getRoot(e[2])
    if x != y:
        sumLength += e[0]
        rootList[x] = rootList[y] = min(x, y)
print(sumLength)

Python: n = int(raw_input())
a = []

for i in range(n):
    inp = raw_input()
    if "-1" in inp:
        inp = inp.replace("-1","10000")
    a.append(list(map(int, inp.split())))

w = 0
v = set()
v.add(0)

while len(v) < n:
    min_w   = 10000
    min_idx = 0
    i = 0
    for node in v:
        if min_w > min(a[node]):
            min_w = min(a[node])
            i = node
            min_idx = a[i].index(min_w)
    if min_idx in v:
        a[i][min_idx] = 10000
        continue
    else:
        w += min_w
        v.add(min_idx)

print(w)

Python: n=int(input())
M=[list(map(int,input().split()))for _ in[0]*n]
d=[0]+[1e4]*n
b=[1]*n
a=0
while 1:
 u=-1
 for i in range(n):
  if b[i]and(u<0 or d[i]<d[u]):u=i
 if u<0:break
 b[u]=0
 a+=d[u]
 for v in range(n):
  t=M[u][v]
  if t+1 and d[v]>t:d[v]=t
print(a)

Python: def prim(n,M):
    d = [None]*n
    p = [None]*n
    searched = [0]*n
    
    for i in range(n):
        d[i] = float("inf")
        p[i] = -1
    
    d[0] = 0
    
    while True:
        minv = float("inf")
        u = -1
        for i in range(n):
            if minv > d[i] and not searched[i]:
                u = i
                minv = d[i]
        
        if u == -1:
            break
        searched[u] = 1
        for v in range(n):
            if (not searched[v]) and M[u][v] != -1:
                if d[v] > M[u][v]:
                    d[v] = M[u][v]
                    p[v] = u

    s = 0
    for i in range(n):
        if p[i] != -1:
            s += M[i][p[i]]
    return print(s)

n = int(input())
M = [list(map(int,input().split())) for _ in range(n)]
prim(n,M)

Python: #!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys

WHITE, GRAY, BLACK = 0, 1, 2


def prim_span_tree():
    min_weight_vertices[0] = 0

    while True:
        min_cost = 2001
        current_vertex = -1
        for i in range(vertices_num):
            if color[i] != BLACK and min_weight_vertices[i] < min_cost:
                min_cost = min_weight_vertices[i]
                current_vertex = i

        if min_cost == 2001:
            break

        color[current_vertex] = BLACK

        for j in range(vertices_num):
            v_weight = int(init_vertices_matrix[current_vertex][j])
            if color[j] != BLACK and v_weight >= 0:
                if v_weight < min_weight_vertices[j]:
                    min_weight_vertices[j] = v_weight
                    parent_list[j] = current_vertex
                    color[j] = GRAY

    return min_weight_vertices


if __name__ == '__main__':
    _input = sys.stdin.readlines()
    vertices_num = int(_input[0])
    init_vertices_matrix = list(map(lambda x: x.split(), _input[1:]))

    parent_list, min_weight_vertices = [-1] * vertices_num, [2001] * vertices_num
    color = [WHITE] * vertices_num
    ans = prim_span_tree()
    print(sum(ans))