Buggy python submission (verdict: Time Limit Exceeded):
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group(self):
        return [self.members(r) for r in self.roots()]
      
    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

import sys
input = sys.stdin.readline
import heapq

n, m = map(int, input().split())
if m == n-1:
  print(0)
  exit()
if n < 2*(n-m-1):
  print("Impossible")
  exit()
A = tuple(map(int, input().split()))
uf = UnionFind(n)
for _ in range(m):
  x, y = map(int, input().split())
  uf.unite(x, y)
ans = 0
L = []
for l in uf.all_group():
  K = sorted((A[i] for i in l), reverse=True)
  ans += K.pop()
  for k in K:
    heapq.heappush(L, k)
for _ in range(n-m-2):
  ans += heapq.heappop(L)
print(ans)

Fixed submission:
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**7)
import heapq

n, m = map(int, input().split())
if m == n-1:
  print(0)
  exit()
if n < 2*(n-m-1):
  print("Impossible")
  exit()
A = tuple(map(int, input().split()))
G = [[] for _ in range(n)]
for _ in range(m):
  x, y = map(int, input().split())
  G[x].append(y)
  G[y].append(x)
ans = 0
L = []
seen = [False]*n
def dfs(v):
  global ans
  K = []
  stack = [v]
  while stack:
    v = stack.pop()
    heapq.heappush(K, A[v])
    seen[v] = True
    for nv in G[v]:
      if seen[nv]:
        continue
      stack.append(nv)
  ans += heapq.heappop(K)
  for k in K:
    heapq.heappush(L, k)
for i in range(n):
  if not seen[i]:
    dfs(i)
for _ in range(n-m-2):
  ans += heapq.heappop(L)
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group(self):
        return [self.members(r) for r in self.roots()]
      
    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

import sys
input = sys.stdin.readline
import heapq

n, m = map(int, input().split())
if m == n-1:
  print(0)
  exit()
if n < 2*(n-m-1):
  print("Impossible")
  exit()
A = tuple(map(int, input().split()))
uf = UnionFind(n)
for _ in range(m):
  x, y = map(int, input().split())
  uf.unite(x, y)
ans = 0
L = []
for l in uf.all_group():
  K = []
  for i in l:
    heapq.heappush(K, A[i])
  ans += heapq.heappop(K)
  for k in K:
    heapq.heappush(L, k)
for _ in range(n-m-2):
  ans += heapq.heappop(L)
print(ans)

Fixed submission:
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**7)
import heapq

n, m = map(int, input().split())
if m == n-1:
  print(0)
  exit()
if n < 2*(n-m-1):
  print("Impossible")
  exit()
A = tuple(map(int, input().split()))
G = [[] for _ in range(n)]
for _ in range(m):
  x, y = map(int, input().split())
  G[x].append(y)
  G[y].append(x)
ans = 0
L = []
seen = [False]*n
def dfs(v):
  global ans
  K = []
  stack = [v]
  while stack:
    v = stack.pop()
    heapq.heappush(K, A[v])
    seen[v] = True
    for nv in G[v]:
      if seen[nv]:
        continue
      stack.append(nv)
  ans += heapq.heappop(K)
  for k in K:
    heapq.heappush(L, k)
for i in range(n):
  if not seen[i]:
    dfs(i)
for _ in range(n-m-2):
  ans += heapq.heappop(L)
print(ans)