#include<iostream>
#include<algorithm>
using namespace std;
int fa[10010];
int cha(int a) {
	if (fa[a] != a)fa[a] = cha(fa[a]);	//递归实现，路径压缩
	return fa[a];
}

void bing(int a, int b) {
	a = cha(a);							
	b = cha(b);
	fa[a] = b;							//a的师傅是b
}

int main() {							//江湖开始：n个城市，相当于n个门派，两个城市相连，记为a的师傅为b

	int n, m,ans=0,a,b;
	while (cin >> n&&n) {
		ans = 0;
		cin >> m;
		if (m == 0)cout << n - 1 << "\n";
		else if (m == 1)cout << n - 2 << "\n";
		else {
	for (int i = 1; i <= n; i++)		//初始化，假定每个人师傅就是自己
		fa[i] = i;

	for (int i = 1; i <= m; i++) {
		cin >> a >> b;
		bing(a, b);						
	}
	for (int i = 1; i <= n; i++) 
		if (fa[i]==i)ans++;				//师傅是自己的，说明是一个门派
	
	cout << ans-1 << "\n";
		}
	}
	return 0;
}