#include <fstream>
#include <set>
using namespace std;
ifstream f("dfs.in");
ofstream g("dfs.out");
set<int> v[100005];
int n, m, x, y, k = 1;
bool viz[100005];
void dfs(int x, int y) {
    viz[x] = y;
    for (set<int>::iterator it = v[x].begin(); it != v[x].end(); it++) {
        if (!viz[*it]) {
            dfs(*it, y);
        }
    }
}
int main() {
    f >> n >> m;
    for (int i = 1; i <= m; i++) {
        f >> x >> y;
        v[x].insert(y);
        v[y].insert(x);
    }
    for (int i = 1; i <= n; i++) {
        if (viz[i] == 0) {
            dfs(i,k);
            k++;
        }
    }
    g << k - 1;
    return 0;
}