白準2606号:ウイルス

from collections import deque, defaultdict

def bfs(graph,start,visited):
    visited[start] = True

    new_computer = deque([start])

    while new_computer:
        computers = new_computer.popleft()

        for computer in graph[computers]:
            if not visited[computer]:
                new_computer.append(computer)
                visited[computer] = True

N = int(input())
M = int(input())
visited = [False] * (N+1)

graph = defaultdict(list)
for _ in range(M):
    i,j = list(map(int,input().split()))
    graph[i].append(j)
    graph[j].append(i)

bfs(graph,1,visited)
print(sum(visited)-1)