Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
from collections import deque
import sys
try:
    from typing import Deque, List
except ImportError:
    pass


sys.setrecursionlimit(10000000)


def dfs(G: "List[List[int]]", a: int, b: int, par: int = -1):
    for t in G[a]:
        if t == par:
            continue
        if t == b:
            return [t]
        path = dfs(G, t, b, a)
        if path:
            return [t] + path
    return None


def bfs(G: "List[List[int]]", a: int, par: int = -1):
    q = deque()  # type: Deque[int]
    q.append(a)
    visited = {par, a}
    while q:
        s = q.popleft()
        for t in G[s]:
            if t in visited:
                continue
            q.append(t)
            visited.add(t)
    return len(visited) - 1


def solve(N: int, a: "List[int]", b: "List[int]"):
    G = [[] for i in range(N)]
    for ai, bi in zip(a, b):
        ai -= 1
        bi -= 1
        G[ai].append(bi)
        G[bi].append(ai)
    path = dfs(G, 0, N - 1)
    assert path
    path = [0] + path
    bb = path[(len(path) - 1) // 2]
    wb = path[(len(path) + 1) // 2]
    bn = bfs(G, bb, wb)
    wn = bfs(G, wb, bb)
    if bn > wn:
        print("Fennec")
    else:
        print("Snuke")


def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    a = [int()] * (N - 1)  # type: "List[int]"
    b = [int()] * (N - 1)  # type: "List[int]"
    for i in range(N - 1):
        a[i] = int(next(tokens))
        b[i] = int(next(tokens))
    solve(N, a, b)


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
from collections import deque
import sys
try:
    from typing import Deque, List
except ImportError:
    pass


def bfs(G: "List[List[int]]", a: int):
    q = deque()  # type: Deque[int]
    q.append(a)
    dist = [-1] * len(G)
    dist[a] = 0
    while q:
        s = q.popleft()
        for t in G[s]:
            if dist[t] >= 0:
                continue
            q.append(t)
            dist[t] = dist[s] + 1
    return dist


def solve(N: int, a: "List[int]", b: "List[int]"):
    G = [[] for i in range(N)]
    for ai, bi in zip(a, b):
        ai -= 1
        bi -= 1
        G[ai].append(bi)
        G[bi].append(ai)
    db = bfs(G, 0)
    dw = bfs(G, N - 1)
    bn = sum((dbi <= dwi) for dbi, dwi in zip(db, dw))
    wn = N - bn
    if bn > wn:
        print("Fennec")
    else:
        print("Snuke")


def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    a = [int()] * (N - 1)  # type: "List[int]"
    b = [int()] * (N - 1)  # type: "List[int]"
    for i in range(N - 1):
        a[i] = int(next(tokens))
        b[i] = int(next(tokens))
    solve(N, a, b)


if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
#!/usr/bin/env python3
from collections import deque
import sys
try:
    from typing import Deque, List
except ImportError:
    pass


def dfs(G: "List[List[int]]", a: int, b: int, par: int = -1):
    for t in G[a]:
        if t == par:
            continue
        if t == b:
            return [t]
        path = dfs(G, t, b, a)
        if path:
            return [t] + path
    return None


def bfs(G: "List[List[int]]", a: int, par: int = -1):
    q = deque()  # type: Deque[int]
    q.append(a)
    visited = {par, a}
    while q:
        s = q.popleft()
        for t in G[s]:
            if t in visited:
                continue
            q.append(t)
            visited.add(t)
    return len(visited) - 1


def solve(N: int, a: "List[int]", b: "List[int]"):
    G = [[] for i in range(N)]
    for ai, bi in zip(a, b):
        ai -= 1
        bi -= 1
        G[ai].append(bi)
        G[bi].append(ai)
    path = dfs(G, 0, N - 1)
    assert path
    path = [0] + path
    bb = path[(len(path) - 1) // 2]
    wb = path[(len(path) + 1) // 2]
    bn = bfs(G, bb, wb)
    wn = bfs(G, wb, bb)
    if bn > wn:
        print("Fennec")
    else:
        print("Snuke")


def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    a = [int()] * (N - 1)  # type: "List[int]"
    b = [int()] * (N - 1)  # type: "List[int]"
    for i in range(N - 1):
        a[i] = int(next(tokens))
        b[i] = int(next(tokens))
    solve(N, a, b)


if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
from collections import deque
import sys
try:
    from typing import Deque, List
except ImportError:
    pass


def bfs(G: "List[List[int]]", a: int):
    q = deque()  # type: Deque[int]
    q.append(a)
    dist = [-1] * len(G)
    dist[a] = 0
    while q:
        s = q.popleft()
        for t in G[s]:
            if dist[t] >= 0:
                continue
            q.append(t)
            dist[t] = dist[s] + 1
    return dist


def solve(N: int, a: "List[int]", b: "List[int]"):
    G = [[] for i in range(N)]
    for ai, bi in zip(a, b):
        ai -= 1
        bi -= 1
        G[ai].append(bi)
        G[bi].append(ai)
    db = bfs(G, 0)
    dw = bfs(G, N - 1)
    bn = sum((dbi <= dwi) for dbi, dwi in zip(db, dw))
    wn = N - bn
    if bn > wn:
        print("Fennec")
    else:
        print("Snuke")


def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    a = [int()] * (N - 1)  # type: "List[int]"
    b = [int()] * (N - 1)  # type: "List[int]"
    for i in range(N - 1):
        a[i] = int(next(tokens))
        b[i] = int(next(tokens))
    solve(N, a, b)


if __name__ == '__main__':
    main()