#include <iostream>
#include <bits/stdc++.h>
#define MAXN 100005
using namespace std;
vector <int> lista[MAXN];
int conex[MAXN], viz[MAXN], compCon = 1;

void DFS(int nod,int n){

    int i, len;
    len = lista[nod].size();
    viz[nod] = 1;
    conex[nod] = compCon;

    for(i = 0;i < len; ++i)
        if(viz[lista[nod][i]] == 0)
            DFS(lista[nod][i],n);
}

int main(){

    FILE *f, *g;
    f = fopen("dfs.in","r");
    g = fopen("dfs.out","w");
    int n, m, i, x, y;

    fscanf(f,"%d %d",&n,&m);
    for(i = 1;i <= m; ++i){
        fscanf(f,"%d %d",&x,&y);
        lista[x].push_back(y);
        lista[y].push_back(x);
    }

    for(i = 1;i <= n; ++i)
        viz[i] = 0;

    for(i = 1;i <= n; ++i)
        if(viz[i] == 0){
            DFS(i,n);
            ++compCon;
        }
    fprintf(g,"%d",compCon - 1);


}