Baekjoon-2606-바이러스

from re import L
import sys
input = sys.stdin.readline

N = int(input())
E = int(input())

graph = [[] for _ in range(N+1)]
for _ in range(E):
    u,v = map(int, input().split())
    graph[u].append(v)
    graph[v].append(u)

queue = [1]
visited = [0 for _ in range(N+1)]
visited[1] = 1 
count = -1
while queue:
    node = queue.pop(0)
    count += 1
    for child in graph[node]:
        if visited[child] == 0:
            queue.append(child)
            visited[child] = 1
    
print(count)