#include <bits/stdc++.h>
#define all(x)                x.begin(),x.end()
#define pb                    push_back
#define IOfast                ios_base::sync_with_stdio(false); cin.tie(NULL);
using namespace std;

//dsu struct 1 is the starting

struct dsu_struct
{
  vector<int> par; //parent of node
  int total_comp;  //total component

  void init(int n)
  { //index 1 is the starting
    total_comp = n;
    par.resize(n+1);
    for(int i=1;i<=n;i++) par[i] = i;
  }

  int get_super_parent(int x)
  {
    if(par[x] == x) return x;
    else return par[x] = get_super_parent(par[x]);
  }

  void merge(int x,int y)
  {
    int super_par_x = get_super_parent(x);
    int super_par_y = get_super_parent(y);

    if(super_par_x != super_par_y)
    {
      par[super_par_x]=super_par_y;
      total_comp--;
    }
  }
};

void solve()
{
  int n,m;
  cin>>n>>m;
  dsu_struct dsu;
  dsu.init(n);
  while(m--)
  {
    int u,v;
    cin>>u>>v;
    dsu.merge(u,v);
  }
  cout<<dsu.total_comp - 1<<"\n";
  for(int i=1;i<n;i++)
  {
    if(dsu.get_super_parent(i) != dsu.get_super_parent(i + 1))
      cout<<i<<" "<<i+1<<"\n";
     dsu.merge(i,i+1);
  }
}

int main()
{
  IOfast;
  solve();
  return 0;
}