#include <cstdio>

using namespace std;

int n,m,a[1005][1005],viz[1005];

void Read()
{
    int x,y;
    freopen("dfs.in","r",stdin);
    freopen("dfs.out","w",stdout);
    scanf("%i %i",&n,&m);
    for(int i=1;i<=m;i++)
    {
        scanf("%i %i",&x,&y);
        a[x][y]=a[y][x]=1;
    }
}

void Parcurgere(int nod)
{
    viz[nod] = 1;
    for(int i=1;i<=n;i++)
    {
        if(viz[i] == 0 && a[nod][i] == 1)
            Parcurgere(i);
    }
}

int main()
{
    int k=1;
    Read();
    for(int i=1;i<=n;i++)
        if(viz[i]==0)
        {
            Parcurgere(i);
            k++;
        }
    printf("%i",--k);
    return 0;
}