Buggy python submission (verdict: Runtime Error):
N = int(input())
edge = [[] for _ in range(N+1)]
for _ in range(N-1):
    a,b,c = map(int,input().split())
    edge[a].append((b,c))
    edge[b].append((a,c))
Q,K = map(int,input().split())
distance = [None] * (N+1)
def dfs(v1,d):
    distance[v1] = d
    for v2,dd in edge[v1]:
        if distance[v2] is not None:
            continue
        dfs(v2,d+dd)

dfs(K,0)

ans = [0] * Q
for i in range(Q):
    x,y = map(int,input().split())
    ans[i] = distance[x]+distance[y]
for a in ans:
    print(a)


Fixed submission:
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**6)
N = int(input())
edge = [[] for _ in range(N+1)]
for _ in range(N-1):
    a,b,c = map(int,input().split())
    edge[a].append((b,c))
    edge[b].append((a,c))
Q,K = map(int,input().split())
distance = [None] * (N+1)
def dfs(v1,d):
    distance[v1] = d
    for v2,dd in edge[v1]:
        if distance[v2] is not None:
            continue
        dfs(v2,d+dd)

dfs(K,0)

ans = [0] * Q
for i in range(Q):
    x,y = map(int,input().split())
    ans[i] = distance[x]+distance[y]
for a in ans:
    print(a)

Buggy python submission (verdict: Runtime Error):
N = int(input())
edge = [[] for _ in range(N+1)]
for _ in range(N-1):
    a,b,c = map(int,input().split())
    edge[a].append((b,c))
    edge[b].append((a,c))
Q,K = map(int,input().split())
distance = [-1] * (N+1)
def dfs(v1,d):
    distance[v1] = d
    for v2,dd in edge[v1]:
        if distance[v2] is not -1:
            continue
        dfs(v2,d+dd)

dfs(K,0)

ans = [0] * Q
for i in range(Q):
    x,y = map(int,input().split())
    ans[i] = distance[x]+distance[y]
for a in ans:
    print(a)


Fixed submission:
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**6)
N = int(input())
edge = [[] for _ in range(N+1)]
for _ in range(N-1):
    a,b,c = map(int,input().split())
    edge[a].append((b,c))
    edge[b].append((a,c))
Q,K = map(int,input().split())
distance = [None] * (N+1)
def dfs(v1,d):
    distance[v1] = d
    for v2,dd in edge[v1]:
        if distance[v2] is not None:
            continue
        dfs(v2,d+dd)

dfs(K,0)

ans = [0] * Q
for i in range(Q):
    x,y = map(int,input().split())
    ans[i] = distance[x]+distance[y]
for a in ans:
    print(a)

Buggy python submission (verdict: Runtime Error):
N = int(input())
edge = [[] for _ in range(N+1)]
for _ in range(N-1):
    a,b,c = map(int,input().split())
    edge[a].append((b,c))
    edge[b].append((a,c))
Q,K = map(int,input().split())
distance = [-1] * (N+1)
def dfs(v1,d):
    distance[v1] = d
    for v2,dd in edge[v1]:
        if distance[v2] is not -1:
            continue
        dfs(v2,d+dd)

dfs(K,0)
print(distance)
ans = [0] * Q
for i in range(Q):
    x,y = map(int,input().split())
    ans[i] = distance[x]+distance[y]
for a in ans:
    print(a)


Fixed submission:
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**6)
N = int(input())
edge = [[] for _ in range(N+1)]
for _ in range(N-1):
    a,b,c = map(int,input().split())
    edge[a].append((b,c))
    edge[b].append((a,c))
Q,K = map(int,input().split())
distance = [None] * (N+1)
def dfs(v1,d):
    distance[v1] = d
    for v2,dd in edge[v1]:
        if distance[v2] is not None:
            continue
        dfs(v2,d+dd)

dfs(K,0)

ans = [0] * Q
for i in range(Q):
    x,y = map(int,input().split())
    ans[i] = distance[x]+distance[y]
for a in ans:
    print(a)

Buggy python submission (verdict: Runtime Error):
N = int(input())
edge = [[] for _ in range(N+1)]
for _ in range(N-1):
    a,b,c = map(int,input().split())
    edge[a].append((b,c))
    edge[b].append((a,c))
Q,K = map(int,input().split())
distance = [-1] * (N+1)
def dfs(v1,d):
    distance[v1] = d
    for v2,dd in edge[v1]:
        if distance[v2] != -1:
            continue
        else:
            dfs(v2,d+dd)

dfs(K,0)
ans = [0] * Q
for i in range(Q):
    x,y = map(int,input().split())
    ans[i] = distance[x]+distance[y]
for a in ans:
    print(a)


Fixed submission:
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**6)
N = int(input())
edge = [[] for _ in range(N+1)]
for _ in range(N-1):
    a,b,c = map(int,input().split())
    edge[a].append((b,c))
    edge[b].append((a,c))
Q,K = map(int,input().split())
distance = [None] * (N+1)
def dfs(v1,d):
    distance[v1] = d
    for v2,dd in edge[v1]:
        if distance[v2] is not None:
            continue
        dfs(v2,d+dd)

dfs(K,0)

ans = [0] * Q
for i in range(Q):
    x,y = map(int,input().split())
    ans[i] = distance[x]+distance[y]
for a in ans:
    print(a)