바이러스(백준)

import sys
from collections import deque
def dfs(graph, v, visited):
    
    visited[v] = True
    
    
    for i in graph[v]:
        if not visited[i]:
            dfs(graph, i, visited)
            

    
n= int(input())
m = int(input())
path =[[] for x in range(n+1)]

for i in range(m):
    a,b = map(int, sys.stdin.readline().split())
    path[a].append(b)
    path[b].append(a)

path =[sorted(x) for x in path]

visited = [False]*len(path)
dfs(path,1,visited)
count =0
for ele in visited:
    if ele == True:
        count +=1
print(count -1)