hdu_1232

/*并查集裸题*/
#include <cstdio>
#include <cstring>

#define MAXN	1001

int root[MAXN], hash[MAXN];

int get_root(int x)
{
	if( root[x] == x ) {
		return x;
	}
	return root[x] = get_root(root[x]);
}

int main(int argc, char const *argv[])
{
#ifndef ONLINE_JUDGE
	freopen("test.in", "r", stdin);
#endif
	int vertex, arc, u, v, r_x, r_y, ans;
	while( scanf("%d", &vertex) && vertex ) {
		scanf("%d", &arc);
		for(int i = 1; i <= vertex; i++) {
			root[i] = i;
		}
		for(int i = 0; i < arc; i ++) {
			scanf("%d %d", &u, &v);
			r_x = get_root(u);	r_y = get_root(v);
			if( r_x != r_y ) {
				root[r_x] = r_y;
			}
		}
		ans = 0;	memset(hash, 0, sizeof(hash));
		for(int i = 1; i <= vertex; i ++) {
			root[i] = get_root(i);
			hash[root[i]] ++;
		}
		for(int i = 1; i <= vertex; i ++) {
			if( hash[i] ) {
				ans ++;
			}
		}
		printf("%d\n", ans-1);
	}
	return 0;
}