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#include <bits/stdc++.h>
using namespace std;
const int SIZE=101000;
void imax(int &a, int b){
a=max(a, b);
}
void imin(int &a, int b){
a=min(a, b);
}
void lmax(long long &a, long long b){
a=max(a, b);
}
void lmin(long long &a, long long b){
a=min(a, b);
}
/*
WARNING: I'm using strange bracket style!
*/
vector <pair <int, int> > out;
vector <int> v[SIZE], s;
int n, q, x, y;
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin>>n>>q;
while (q--)
cin>>x>>y, v[min(x, y)].push_back(max(x, y));
v[1].push_back(n);
for (int i=1; i<=n; i++)
{
sort(v[i].begin(), v[i].end());
reverse(v[i].begin(), v[i].end());
while (!s.empty() && s.back()<=i)
s.pop_back();
if (!s.empty() && s.back()>i+1)
if (v[i].size()==0 || s.back()!=v[i][0])
out.push_back({s.back(), i});
for (auto j: v[i])
s.push_back(j);
}
cout<<out.size()<<"\n";
for (auto i: out)
cout<<i.first<<" "<<i.second<<"\n";
return 0;
}
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