[DFS/BFS-2606号]ウイルス

from collections import deque
import sys

n = int(input())
pair = int(input())

graph = [[]*n for _ in range(n+1)]
cnt = 0
visited = [False]*(n+1)

for _ in range(pair):
    x, y = map(int, sys.stdin.readline().split())
    graph[x].append(y)
    graph[y].append(x)


def dfs(n):
    global cnt
    visited[n] = True
    for i in graph[n]:
        if visited[i] == False:
            dfs(i)
            cnt += 1


dfs(1)
print(cnt)