#include <bits/stdc++.h>
#define eps 1e-1
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
const ll fix=(ll)1e10;



multiset<pair<ll, ll>> mset;

int main(){
    ifstream fin("cover.in");
    ofstream fout("cover.out");
    ll n, m;
    fin >> n;
    ll a, b;
    fin >> a >> b;
    while (a!=0 || b!=0) {
        ll tmp=a;
        a=min(a, b);
        b=max(tmp, b);
        mset.insert({a, b});
        fin >> a >> b;
    }

    set<pair<ll, ll>> res1;
    pair<ll, ll> prevPair = *mset.begin();
    ll beg=0;
    ll end=0;
    beg = prevPair.first;
    end = prevPair.second;
    for (auto&s:mset){
        if (end<s.first){
            res1.insert({beg,end});
            prevPair=s;
            end=s.second;
            beg=s.first;
        }

        beg=min(beg,s.first);
        end=max(end,s.second);
        if (s==*mset.rbegin())
            res1.insert({beg, end});
    }
    bool boo=false;
    for (auto&re:res1)
        if (re.first<=0 && re.second>=n)
            boo=true;

    if (!boo){
        fout << "No solution";
        return 0;
    }



    set<pair<ll, ll>> res;
    ll prevbord=(ll)-1e9;
    ll bord=0;
    while(true){
        ll maxCov=0;
        pair<ll,ll> maxPair={0,0};
        for (set<pair<ll, ll>>::iterator it = mset.lower_bound({prevbord, prevbord}); it!=mset.upper_bound({bord+1,bord+1}); ++it){
            if (((*it).second>maxCov)){
                maxCov=(*it).second;
                maxPair = (*it);
            }
        }
        res.insert(maxPair);
        prevbord=bord;
        bord=maxPair.second;
        if (bord>=n)
            break;
    }
    fout << res.size() << '\n';
    for (auto&re:res)
        fout << re.first << " " << re.second << '\n';
    fin.close();
    fout.close();
    return 0;
}