Oving8

import sys
from collections import deque


class Node:
    def __init__(self):
        self.child = []
        self.ratatosk = False
        self.depth = 0


def dfs(root):
    stack = deque([root])

    while stack:
        current = stack.pop()

        if current.ratatosk:
            return current.depth

        for n in current.child:
            if n != None:
                n.depth = current.depth + 1
                stack.append(n)


def bfs(root):
    queue = deque([root])

    while queue:
        current = queue.pop()

        if current.ratatosk:
            return current.depth

        for n in current.child:
            if n != None:
                n.depth = current.depth + 1
                queue.appendleft(n)


def main():
 sys.stdin.readline(),sys.stdin.readline()
 level=0
 d=dict()
 root=sys.stdin.readline().strip()
 ratatosk=sys.stdin.readline().strip()
 for line in sys.stdin:
  children=line.split()
  parent=children.pop(0)
  for child in children:
   d[child]=parent
  while ratatosk in d:
   ratatosk=d[ratatosk]
   level+=1
  if(ratatosk==root):
   return level
print(main())