#include <bits/stdc++.h>
#define MaxN 100001
using namespace std;

ifstream fin("dfs.in");
ofstream fout("dfs.out");

#define cin fin
#define cout fout

int n, m, x, y, contor;
vector <int> v[MaxN];
int viz[MaxN];

void read()
{
    cin >> n >> m;
    for(int i=1; i<=m; i++)
    {
        cin >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
}

void DFS(int nod, int contor)
{
    viz[nod] = contor;
    for(const auto& p : v[nod])
    {
        if(!viz[p])
        {
            DFS(p, contor);
        }
    }
}

int exista()
{
    for(int i=1; i<=n; i++)
    {
        if(viz[i] == 0)
        {
            return i;
        }
    }
    return 0;
}

void solve()
{
    contor = 1;
    while(exista())
    {
        DFS(exista(), contor++);
    }

    cout << contor - 1;
}

int main()
{
    read();
    solve();
}