180207_2606_바이러스

	//https://www.acmicpc.net/problem/2606 #include <iostream>
	#include <queue>
	using namespace std;
	int N, M, cnt;
	bool network[101][101];
	bool visited[101];
	void input(){
	cin >> N >> M;
	int a,b;
	for(int i=0; i<M; i++){
	cin >> a >> b;
	network[a][b]=network[b][a]=1;
	}
	}
	void bfs(){
	queue<int> q;
	q.push(1);
	visited[1]=1;
	while(!q.empty()){
	int now=q.front();
	q.pop();
	for(int i=2; i<=N; i++){
	if(network[now][i] && !visited[i]){
	q.push(i);
	visited[i]=1;
	cnt++;
	}
	}
	}
	}
	int main(){
	input();
	bfs();
	cout << cnt;
	}