// compile: g++ -o data data.cpp -std=gnu++20 -DLOCAL -g
// run: ./data < data.in
#include <bits/stdc++.h>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#ifdef LOCAL
#endif
#define sz(v) ((int)(v).size())
#define PV(v) for (int i=0;i<v.size();++i)cout<<v[i]<<" ";cout<<endl;
#define OK cout<<"OK"<<endl;
#define INTINF 9223372036854775807
#define int long long
#define MAXN 100010

using namespace std;

int n, m;
vector<int> e[MAXN];
vector<int> c[MAXN];
int vis[MAXN];
int cnt = 0;

void dfs(int u, int k) {
    vis[u] = 1;
    c[k].push_back(u);
    for (int v: e[u]) {
        if (vis[v]) continue;
        dfs(v, k);
    }
}

int32_t main() {
    ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);

    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int u, v; cin >> u >> v;
        e[u].push_back(v);
        e[v].push_back(u);
    }
    for (int i = 1; i <= n; ++i) {
        if (!vis[i]) dfs(i, cnt++);
    }
    cout << cnt - 1 << endl;
    for (int i = 0; i < cnt-1; ++i) {
        cout << c[i][0] << " " << c[i+1][0] << endl;
    }

    return 0;
}