#include<cstdio>

#include<cstring>

#include<iostream>

#include<algorithm>

using namespace std;

int n,m,ans;

int fa[],vis[];

int find(int x){

    if(fa[x]==x)    return x;

    else return fa[x]=find(fa[x]);

}

int main(){

    scanf("%d%d",&n,&m);

    for(int i=;i<=n;i++)    fa[i]=i;

    for(int i=;i<=m;i++){

        int x,y;

        scanf("%d%d",&x,&y);

        int dx=find(x);

        int dy=find(y);

        if(dx==dy)    continue;

        fa[dy]=dx;

    }

    for(int i=;i<=n;i++)

        if(!vis[find(i)])    vis[find(i)]=,ans++;

    cout<<ans-;

}