#include <stdio.h>
#include <stdlib.h>
#define MAXN 100001
int con=1,ind[MAXN],next[4*MAXN],y[4*MAXN],viz[MAXN];
void DFS(int nod){
    int p;
    viz[nod]=con;
    p=ind[nod];
    while(p>0){
        if(viz[y[p]]==0)
            DFS(y[p]);
        p=next[p];
    }
}
int main(){
    FILE*fi,*fout;
    int i,n,m,p,x;
    fi=fopen("dfs.in" ,"r");
    fout=fopen("dfs.out" ,"w");
    fscanf(fi,"%d%d" ,&n,&m);
    p=1;
    for(i=1;i<=m;i++){
        fscanf(fi,"%d%d" ,&x,&y[p]);
        if(x!=y[p]){
            next[p]=ind[x];
            ind[x]=p;
            p++;
            next[p]=ind[y[p]];
            ind[y[p]]=p;
            p++;
        }
    }
    for(i=1;i<=n;i++)
        if(viz[i]==0){
            DFS(i);
            con++;
        }
    fprintf(fout,"%d" ,con-1);
    fclose(fi);
    fclose(fout);
    return 0;
}