#1~#10全TLE求调

#include <bits/stdc++.h>
using namespace std;
int fa[1000001], n, m, x, y;
int find(int x){
    if(x != fa[x]) {
        fa[x] = find(fa[x]);
    }
    return fa[x];
}
void unity(int x, int y){
    int r1 = find(x); 
    int r2 = find(y); 
    fa[r1] = r2;
}
int main(){
	while(true){
		int ans = 0;
		scanf("%d", &n);
		if(n == 0){
		}
		scanf("%d", &m);
	    for(int i = 1; i <= n; i++){
	        fa[i] = i; 
	    }
	    for(int i = 1; i <= m; i++){
	        scanf("%d %d", &x, &y);
	        unity(x, y); 
	    }
	    for(int i = 1; i <= n; i++){
	    	if(find(i) == i){
	    		ans++;
			}
		}
		printf("%d\n", ans - 1); 
	}
}