Buggy python submission (verdict: Runtime Error):
from collections import deque
import sys
INF = 11414191981036436433-4

n = int(input())
g = [[] for i in range(n)]
for v in range(n-1):
    a,b,c = map(int,input().split())
    g[a-1].append((b-1,c))
    g[b-1].append((a-1,c))
    
q,k = map(int,input().split())
k -= 1

r = [INF]*n
que = deque([k])
r[k] = 0
while que:
    v = que.popleft()
    rr = r[v]
    for w,x in G[v]:
        if r[w] == INF:
            r[w] = rr + x
            que.append(w)
            
for i in range(q):
    d,e = map(int,input().split())
    print(r[d-1] + r[e-1])

Fixed submission:
from collections import deque
import sys
INF = 11414191981036436433-4

n = int(input())
g = [[] for i in range(n)]
for v in range(n-1):
    a,b,c = map(int,input().split())
    g[a-1].append((b-1,c))
    g[b-1].append((a-1,c))
    
q,k = map(int,input().split())
k -= 1

r = [INF]*n
que = deque([k])
r[k] = 0
while que:
    v = que.popleft()
    rr = r[v]
    for w,x in g[v]:
        if r[w] == INF:
            r[w] = rr + x
            que.append(w)
            
for i in range(q):
    d,e = map(int,input().split())
    print(r[d-1] + r[e-1])

Buggy python submission (verdict: Runtime Error):
from collections import deque
import sys

N = int(input())
prv = [None]*N
G = [[] for i in range(N)]
for v in range(N-1):
    a,b,c = map(int,input().split())
    aa = min(a,b)-1
    bb = max(a,b)-1
    G[aa].append((bb,c))
    prv[bb] = aa

depth = [0]*N
r = [0]*N
que = deque([0])
while que:
    v = que.popleft()
    d = depth[v]
    rr = r[v]
    for w,x in G[v]:
        depth[w] = d + 1
        r[w] = rr + x
        que.append(w)
        
LV = (N-1).bit_length()
def construct(prv):
    kprv = [prv]
    S = prv
    for k in range(LV):
        T = [0]*N
        for i in range(N):
            if S[i] is None:
                continue
            T[i] = S[S[i]]
        kprv.append(T)
        S = T
    return kprv

def lca(u, v, kprv, depth):
    dd = depth[v] - depth[u]
    if dd < 0:
        u, v = v, u
        dd = -dd

    # assert depth[u] <= depth[v]
    for k in range(LV+1):
        if dd & 1:
            v = kprv[k][v]
        dd >>= 1

    # assert depth[u] == depth[v]
    if u == v:
        return u

    for k in range(LV-1, -1, -1):
        pu = kprv[k][u]; pv = kprv[k][v]
        if pu != pv:
            u = pu; v = pv

    # assert kprv[0][u] == kprv[0][v]
    return kprv[0][u]


kprv = construct(prv)

Q,k = map(int, input().split())
k -= 1
for q in range(Q):
    u, v = map(int, input().split())
    u -= 1
    v -= 1
    a1 = lca(u, k, kprv, depth)
    a2 = lca(v, k, kprv, depth)
    aa1 = r[u] + r[k] - 2*r[a1]
    aa2 = r[k] + r[v] - 2*r[a2]
    print(aa1+aa2)

Fixed submission:
from collections import deque
import sys
INF = 11414191981036436433-4

n = int(input())
g = [[] for i in range(n)]
for v in range(n-1):
    a,b,c = map(int,input().split())
    g[a-1].append((b-1,c))
    g[b-1].append((a-1,c))
    
q,k = map(int,input().split())
k -= 1

r = [INF]*n
que = deque([k])
r[k] = 0
while que:
    v = que.popleft()
    rr = r[v]
    for w,x in g[v]:
        if r[w] == INF:
            r[w] = rr + x
            que.append(w)
            
for i in range(q):
    d,e = map(int,input().split())
    print(r[d-1] + r[e-1])