#include <fstream>
#include <vector>
#define DIM 100001
using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");
int n,m,x,y,cnt;
vector<int> l[DIM];
bool viz[DIM];

void dfs(int nod) {
    viz[nod]=1;
    for (unsigned int i=0;i<l[nod].size();i++)
        if (viz[l[nod][i]]==0)
            dfs(l[nod][i]);
}

int main() {
    fin>>n>>m;
    while (m--) {
        fin>>x>>y;
        l[x].push_back(y);
        l[y].push_back(x);
    }
    dfs(1);
    for (int i=1;i<=n;i++)
        if (viz[i]==0)
            cnt++;
    fout<<cnt;
    return 0;
}