Problem:
Score : 400 points

Problem Statement

On a planet far, far away, M languages are spoken. They are conveniently numbered 1 through M.

For CODE FESTIVAL 20XX held on this planet, N participants gathered from all over the planet.

The i-th (1≦i≦N) participant can speak K_i languages numbered L_{i,1}, L_{i,2}, ..., L_{i,{}K_i}.

Two participants A and B can communicate with each other if and only if one of the following conditions is satisfied:

There exists a language that both A and B can speak.

There exists a participant X that both A and B can communicate with.

Determine whether all N participants can communicate with all other participants.

Constraints

2≦N≦10^5

1≦M≦10^5

1≦K_i≦M

(The sum of all K_i)≦10^5

1≦L_{i,j}≦M

L_{i,1}, L_{i,2}, ..., L_{i,{}K_i} are pairwise distinct.

Partial Score

200 points will be awarded for passing the test set satisfying the following: N≦1000, M≦1000 and (The sum of all K_i)≦1000.

Additional 200 points will be awarded for passing the test set without additional constraints.

Input

The input is given from Standard Input in the following format:

N M
K_1 L_{1,1} L_{1,2} ... L_{1,{}K_1}
K_2 L_{2,1} L_{2,2} ... L_{2,{}K_2}
:
K_N L_{N,1} L_{N,2} ... L_{N,{}K_N}

Output

If all N participants can communicate with all other participants, print YES. Otherwise, print NO.

Sample Input 1

4 6
3 1 2 3
2 4 2
2 4 6
1 6

Sample Output 1

YES

Any two participants can communicate with each other, as follows:

Participants 1 and 2: both can speak language 2.

Participants 2 and 3: both can speak language 4.

Participants 1 and 3: both can communicate with participant 2.

Participants 3 and 4: both can speak language 6.

Participants 2 and 4: both can communicate with participant 3.

Participants 1 and 4: both can communicate with participant 2.

Note that there can be languages spoken by no participant.

Sample Input 2

4 4
2 1 2
2 1 2
1 3
2 4 3

Sample Output 2

NO

For example, participants 1 and 3 cannot communicate with each other.

Solution in Python (3.4.3) (judge verdict: Accepted)

import bisect
import copy
import heapq
import sys
import itertools
import queue
from collections import deque
input = sys.stdin.readline
sys.setrecursionlimit(1000000)
mod = 10 ** 9 + 7

def read_values(): return map(int, input().split())
def read_index(): return map(lambda x: int(x) - 1, input().split())
def read_list(): return list(read_values())
def read_lists(N): return [read_list() for n in range(N)]
def init_dp1(init, N): return [init for _ in range(N)]
def init_dp2(init, N, M): return [[init for _ in range(M)] for _ in range(N)]


class V:
    def __init__(self, f, v=None):
        self.f = f
        self.v = v
 
    def __str__(self):
        return str(self.v)
 
    def ud(self, n):
        if n is None:
            return

        if self.v is None:
            self.v = n
            return
        self.v = self.f(self.v, n) 


class UF:
    def __init__(self, N):
        self.parent = [i for i in range(N)]
    
    def get_parent(self, a):
        p = self.parent[a]
        if a == p:
            return a
        
        q = self.get_parent(p)
        self.parent[a] = q
        return q

    def make_pair(self, a, b):
        pa = self.get_parent(a)
        pb = self.get_parent(b)
        if pa == pb:
            return
        
        self.parent[pa] = pb
        self.parent[a] = pb
    
    def is_pair(self, a, b):
        return self.get_parent(a) == self.get_parent(b)


def main():
    N, M = read_values()
    uf = UF(N + M)
    for i in range(N):
        L = read_list()
        for l in L[1:]:
            uf.make_pair(i, l - 1 + N)

    for n in range(1, N):
        if not uf.is_pair(0, n):         
            print("NO")
            return
    print("YES")


if __name__ == "__main__":
    main()