//  Building Roads

#include<bits/stdc++.h>

using namespace std;

void dfs(vector<vector<int>> &g, int s, vector<bool> &v) {
    v[s] = true;
    for (auto e: g[s]) {
        if (!v[e]) dfs(g, e, v);
    }
}


int main() {
    int n, m; cin >> n >> m;
    vector<vector<int>> g(n);
    for (int i{}; i < m; i++) {
        int a, b;
        cin >> a >> b;
        a--; b--;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    int count = -1;
    vector<pair<int, int>> roads;
    vector<bool> v(n);
    for (int i{}; i < n; i++) {
        if (v[i]) continue;
        count ++;
        dfs(g, i, v);
        if (i > 0) roads.push_back({i, i - 1});
    }

    cout << count << endl;
    for (auto [x, y]: roads) {
        cout << x+1 << " " << y + 1 << endl;
    }
    return 0;
}