#include <iostream>
#include <vector>

using namespace std;

struct Adat
{
    vector<int> kezd;
    vector<int> veg;
};

int main()
{
    int n, m;
    cin >> n >> m;
    int hossz = n + m;

    Adat a;

    int MAX = 0;

    for (int i = 0; i < hossz; i++)
    {
        int kezd, veg;
        cin >> kezd >> veg;
        a.kezd.push_back(kezd);
        a.veg.push_back(veg);
        if(MAX < veg)
        {
            MAX = veg;
        }
    }

    vector<vector<int>> vec;
    vec.resize(hossz);
    vector<pair<int,int>> result;
    result.resize(hossz);

    for (int i = 0; i < hossz; i++)
    {
        vec[i].resize(MAX);

        for(int j = 0; j < MAX; j++)
        {
            if(j >= a.kezd[i]-1 && j < a.veg[i])
                vec[i][j] = 1;
            else if(vec[i][j] != 1)
                vec[i][j] = 0;
            //cout << vec[i][j] << ' ';
        }
        //cout << endl;
    }

    int db = 0;
    int veg = 0;
    int k = 0;
    for (int i = 0; i <= MAX; i++)
    {
            int sum = 0;
        for (int j = 0; j < hossz; j++)
        {
            sum += vec[j][i];
        }
        if(sum == 1)
        {
            db++;
            veg = i + 1;
            result[k].first = veg - db + 1;
            result[k].second = veg;
        }
        else
        {
            //cout << veg-db+1 << " " << veg << endl;
            db = 0;
            veg = 0;
            k++;
        }
    }

    int meret = 0;

    for (int i = 0; i <= result.size(); i++)
    {
        if(result[i].first != 0 && result[i].second != 0)
        {
            meret++;
        }
    }

    cout << meret << endl;
    for (int i = 0; i < k; i++)
    {
        if(result[i].first != 0 && result[i].second != 0)
        {
            cout << result[i].first << " " << result[i].second << endl;
        }
    }

    return 0;
}