#include<iostream>
using namespace std;
int p[1000005], r[1000005];
int n,t;
void init()//初始化集合，每个元素的老板都是自己
{for (int i = 1; i <= n; i++){p[i] = i;}
}int find(int x)//查找元素x的老板是谁
{if (x == p[x])return x;elsereturn p[x] = find(p[x]);
}void join(int x, int y)//合并两个集合
{int xRoot = find(x);int yRoot = find(y);if (xRoot == yRoot) //老板相同，不合并return;if (r[xRoot] < r[yRoot]) //r[i]是元素i所在树的高度，矮树的根节点认高树的根节点做老板p[xRoot] = yRoot;else if (r[xRoot] > r[yRoot])p[yRoot] = xRoot;else{p[yRoot] = xRoot;//树高相同，做老板的树高度要加一r[xRoot]++;}
}bool sameRoot(int x, int y)//查询两个元素的老板是否相同
{return find(x) == find(y);
}
int main()
{int m, x, y;while (cin >> n && n != 0){t = 0;cin >> m;init();for (int i = 0; i < m; i++)//把已知联通的元素加入集合
        {cin >> x >> y;if (sameRoot(x, y))continue;elsejoin(x, y);}for (int i = 1; i <= n; i++)//有多少个p[i]==i,就有多少个子集
        {if (p[i] == i)t++;}cout << t-1 << endl;}return 0;
}

#include<iostream>
using namespace std;
int p[1000005], r[1000005];
int n,t,cnt;
void init()//初始化集合，每个元素的老板都是自己
{for (int i = 1; i <= n; i++){p[i] = i;}
}int find(int x)//查找元素x的老板是谁
{if (x == p[x])return x;elsereturn p[x] = find(p[x]);
}void join(int x, int y)//合并两个集合
{int xRoot = find(x);int yRoot = find(y);if (xRoot == yRoot) //老板相同，不合并return;cnt=cnt-1;if (r[xRoot] < r[yRoot]) //r[i]是元素i所在树的高度，矮树的根节点认高树的根节点做老板p[xRoot] = yRoot;else if (r[xRoot] > r[yRoot])p[yRoot] = xRoot;else{p[yRoot] = xRoot;//树高相同，做老板的树高度要加一r[xRoot]++;}
}bool sameRoot(int x, int y)//查询两个元素的老板是否相同
{return find(x) == find(y);
}
int main()
{int m, x, y;while (cin >> n && n != 0){cnt=n;//当元素各不相连的时候，有n个集合t = 0;cin >> m;init();for (int i = 0; i < m; i++)//把已知联通的元素加入集合
        {cin >> x >> y;if (sameRoot(x, y))continue;elsejoin(x, y);}// for (int i = 1; i <= n; i++)//有多少个p[i]==i,就有多少个子集// {//     if (p[i] == i)//         t++;// }cout << cnt-1 << endl;}return 0;
}