# 2606번 바이러스

from collections import deque 

def bfs(start_node, graph):
    queue = deque([start_node])
    visited = set([start_node])

    while queue:
        curr_node = queue.popleft()

        for next_node in graph[curr_node]:
            if next_node not in visited:
                visited.add(next_node)
                queue.append(next_node)
               
    return len(visited)

computer_num = int(input())
network_num = int(input())
computer = {n+1:[] for n in range(computer_num)}
for _ in range(network_num):
    a,b = map(int,input().split())
    computer[a].append(b)
    computer[b].append(a)

print(bfs(1,computer)-1)