#include <fstream>
#include <map>
using namespace std;
ifstream fin("pariuri.in");
ofstream fout("pariuri.out");
int n,q,t,b;
map<int,long long> M;
int main()
{
    fin >> n;
    for(int i=1;i<=n;i++)
    {
        fin >> q;
        for(int i=1;i<=q;i++)
        {
            fin >> t >> b;
            M[t]+=b;
        }
    }
    fout << M.size() << "\n";
    for(map<int,long long>::iterator it=M.begin(); it!=M.end(); ++it)
        fout << (*it).first << " " << (*it).second << " ";
    return 0;
}