最小生成树从何而来

#include <bits/stdc++.h>
using namespace std;
int fa[1005];
int get(int x){
    if(x != fa[x]) fa[x] = get(fa[x]);
    return fa[x];
}
void merge(int x,int y){fa[get(x)] = get(y);}
int main(){
    int n;
	while(cin >> n){
		if(n == 0) return 0;
		int m; cin >> m;
	    for(int i = 1;i <= n;i++) fa[i] = i;
	    for(int i = 1;i <= m;i++){
	        int x,y; cin >> x >> y;
	        merge(x,y);
	    }
        int cnt = 0;
	    for(int i = 1;i <= n;i++){
	    	if(get(i) == i) cnt++;
        }
		cout << cnt - 1 << endl;
	}
    return 0;
}