[백준/Python] 2606 바이러스

computerNo = int(input())
pairNo = int(input())
graph = []
for i in range(101):
    graph.append([])

answer = [0] * 101
answer[1] = 1

for i in range(pairNo):
    a, b = map(int, input().split())
    graph[a].append(b)
    graph[b].append(a)

def dfs(x):
    for i in graph[x]:
        if answer[i]==0:
            answer[i]=1
            dfs(i)

dfs(1)
print(answer.count(1)-1)