#include <cstdio>
#include <iostream>
#define Nmax 2000
using namespace std;
int a[Nmax][Nmax];
int n,m,i,j,cmp=0,c;
bool viz[Nmax];
void reading(int &n,int m)
{
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%d %d",&n,&m);
    int x,y;
   for(i=1;i<=m;++i)
    {
        scanf("%d %d",&x,&y);
        ++a[x][0];a[x][a[x][0]]=y;
        ++a[y][0];a[y][a[y][0]]=x;
    }
}
void dfs(int x)
{
    viz[x]=1;
    for(i=1;i<=a[x][0];++i)
     if (!viz[a[x][i]]) dfs(a[x][i]);
}
int main()
{
    reading(n,m);
    dfs(2);
    ++cmp;
    bool ok;
    do
    {
        ok=false;
        for(i=1;i<=n;++i)
         if (!viz[i]) {ok=true;c=i;++cmp;break;}
         dfs(c);
    }
    while(ok);
    printf("%d",cmp);
    return 0;
}