#include <fstream>
#include <unordered_map>
using namespace std;

ifstream fin("pariuri.in");
ofstream fout("pariuri.out");


unordered_map<int,int> h;
int main()
{
	int n;
	int nr=0;
	fin >> n;
	int min = 1000000000;
	int max = 0;
	for (; n; n--)
	{
		int m;
		fin >> m;
		for (; m; m--)
		{
			int t;
			fin >> t;
			int b;
			fin >> b;
			if (t < min)
				min = t;
			if (t>max)
				max = t;
			if (h.find(t) == h.end())
			{
				nr++;
				h[t] = b;
			}
			else
			{
				h[t] += b;
			}
		}
	}
	fout << nr<<'\n';
	for (int i = min; i <= max; i++)
	{
		if (h.find(i) != h.end())
			fout << i << ' ' << h[i]<<' ';
	}
	
}