Buggy python submission (verdict: Runtime Error):
N = int(input())
G = [[] for i in range(N)]
for i in range(N - 1):
    a, b, c = map(int, input().split())
    a, b = a - 1, b - 1
    G[a].append([b, c])
    G[b].append([a, c])

Q, K = map(int, input().split())
K -= 1
dist = [-1] * N
dist[K] = 0


def dfs(n):
    for v, c in G[n]:
        if dist[v] < 0:
            dist[v] = dist[n] + c
            dfs(v)


dfs(K)
for q in range(Q):
    x, y = map(int, input().split())
    x, y = x - 1, y - 1
    print(dist[x] + dist[y])


Fixed submission:
import sys;sys.setrecursionlimit(int(1e7))

N = int(input())
ABC = [tuple(map(int, input().split())) for i in range(N-1)]
Q, K = map(int, input().split())
XY = [tuple(map(int, input().split())) for i in range(Q)]

tree = [[] for i in range(N+1)]   
depth = [None] * (N+1)

for abc in ABC:
    tree[abc[0]].append((abc[1],abc[2]))
    tree[abc[1]].append((abc[0],abc[2]))
    
def DFS(v, p, d):
    depth[v] = d
    for e in tree[v]:
        if e[0] != p:
            DFS(e[0], v, d + e[1])
            
DFS(K, 0, 0)

for x,y in XY:
    print(depth[x] + depth[y])

Buggy python submission (verdict: Runtime Error):
N = int(input())
ABC = [tuple(map(int, input().split())) for i in range(N-1)]
Q, K = map(int, input().split())
XY = [tuple(map(int, input().split())) for i in range(Q)]

tree = [[] for i in range(N+1)]   
depth = [None] * (N+1)

for abc in ABC:
    tree[abc[0]].append((abc[1],abc[2]))
    tree[abc[1]].append((abc[0],abc[2]))
    
def DFS(v, p, d):
    depth[v] = d
    for e in tree[v]:
        if e[0] != p:
            DFS(e[0], v, d + e[1])
            
DFS(K, 0, 0)

for i in range(Q):
    print(depth[XY[i][0]] + depth[XY[i][1]])

Fixed submission:
import sys;sys.setrecursionlimit(int(1e7))

N = int(input())
ABC = [tuple(map(int, input().split())) for i in range(N-1)]
Q, K = map(int, input().split())
XY = [tuple(map(int, input().split())) for i in range(Q)]

tree = [[] for i in range(N+1)]   
depth = [None] * (N+1)

for abc in ABC:
    tree[abc[0]].append((abc[1],abc[2]))
    tree[abc[1]].append((abc[0],abc[2]))
    
def DFS(v, p, d):
    depth[v] = d
    for e in tree[v]:
        if e[0] != p:
            DFS(e[0], v, d + e[1])
            
DFS(K, 0, 0)

for x,y in XY:
    print(depth[x] + depth[y])

Buggy python submission (verdict: Runtime Error):
N = int(input())
ABC = [tuple(map(int, input().split())) for i in range(N-1)]
Q, K = map(int, input().split())
XY = [tuple(map(int, input().split())) for i in range(Q)]

tree = [[] for i in range(N+1)]   
depth = [None] * (N+1)

for abc in ABC:
    tree[abc[0]].append((abc[1],abc[2]))
    tree[abc[1]].append((abc[0],abc[2]))
    
def DFS(v, p, d):
    depth[v] = d
    for e in tree[v]:
        if e[0] != p:
            DFS(e[0], v, d + e[1])
            
DFS(K, 0, 0)

for x,y in XY:
    print(depth[x] + depth[y])
    

Fixed submission:
import sys;sys.setrecursionlimit(int(1e7))

N = int(input())
ABC = [tuple(map(int, input().split())) for i in range(N-1)]
Q, K = map(int, input().split())
XY = [tuple(map(int, input().split())) for i in range(Q)]

tree = [[] for i in range(N+1)]   
depth = [None] * (N+1)

for abc in ABC:
    tree[abc[0]].append((abc[1],abc[2]))
    tree[abc[1]].append((abc[0],abc[2]))
    
def DFS(v, p, d):
    depth[v] = d
    for e in tree[v]:
        if e[0] != p:
            DFS(e[0], v, d + e[1])
            
DFS(K, 0, 0)

for x,y in XY:
    print(depth[x] + depth[y])

Buggy python submission (verdict: Runtime Error):
N = int(input())
ABC = [tuple(map(int, input().split())) for i in range(N-1)]
Q, K = map(int, input().split())
XY = [tuple(map(int, input().split())) for i in range(Q)]

tree = [[] for i in range(N+1)]   
depth = [None] * (N+1)

for abc in ABC:
    tree[abc[0]].append((abc[1],abc[2]))
    tree[abc[1]].append((abc[0],abc[2]))
    
def DFS(v, p, d):
    depth[v] = d
    for e in tree[v]:
        if e[0] != p:
            DFS(e[0], v, d + e[1])
            
DFS(K, 0, 0)

for xy in XY:
    print(depth[xy[0]] + depth[xy[1]])

Fixed submission:
import sys;sys.setrecursionlimit(int(1e7))

N = int(input())
ABC = [tuple(map(int, input().split())) for i in range(N-1)]
Q, K = map(int, input().split())
XY = [tuple(map(int, input().split())) for i in range(Q)]

tree = [[] for i in range(N+1)]   
depth = [None] * (N+1)

for abc in ABC:
    tree[abc[0]].append((abc[1],abc[2]))
    tree[abc[1]].append((abc[0],abc[2]))
    
def DFS(v, p, d):
    depth[v] = d
    for e in tree[v]:
        if e[0] != p:
            DFS(e[0], v, d + e[1])
            
DFS(K, 0, 0)

for x,y in XY:
    print(depth[x] + depth[y])

Buggy python submission (verdict: Runtime Error):
N = int(input())
ABC = [tuple(map(int, input().split())) for i in range(N-1)]
Q, K = map(int, input().split())
XY = [tuple(map(int, input().split())) for i in range(Q)]

tree = [[] for i in range(N+1)]   
depth = [None] * (N+1)

for abc in ABC:
    tree[abc[0]].append((abc[1],abc[2]))
    tree[abc[1]].append((abc[0],abc[2]))
    
def DFS(v, p, d):
    depth[v] = d
    for e in tree[v]:
        if e[0] != p:
            DFS(e[0], v, d + e[1])
            
DFS(K, -1, 0)

for xy in XY:
    print(depth[xy[0]] + depth[xy[1]])

Fixed submission:
import sys;sys.setrecursionlimit(int(1e7))

N = int(input())
ABC = [tuple(map(int, input().split())) for i in range(N-1)]
Q, K = map(int, input().split())
XY = [tuple(map(int, input().split())) for i in range(Q)]

tree = [[] for i in range(N+1)]   
depth = [None] * (N+1)

for abc in ABC:
    tree[abc[0]].append((abc[1],abc[2]))
    tree[abc[1]].append((abc[0],abc[2]))
    
def DFS(v, p, d):
    depth[v] = d
    for e in tree[v]:
        if e[0] != p:
            DFS(e[0], v, d + e[1])
            
DFS(K, 0, 0)

for x,y in XY:
    print(depth[x] + depth[y])