#include <vector>
#include <cstdio>
#include <iostream>
using namespace std;

struct product
{
    int bandwidth;
    int price;
};

double min_result = 0; 
int cur_i = -1;
int cur_j = -1;
double tmp_result = 0.0;
int tmp_price = 0;
vector< vector<product> > vec;
void get_data( int i )
{
    if( i == vec.size() )
    {
        tmp_result = (double)vec[cur_i][cur_j].bandwidth/tmp_price;
        if( tmp_result > min_result )
            min_result = tmp_result;
        return;
    }


    if( i == cur_i )
    {
        get_data(i+1);
        return;
    }

    for( int j = 0; j < vec[i].size(); ++j )
    {


       if( vec[cur_i][cur_j].bandwidth > vec[i][j].bandwidth )
            continue;

        tmp_price += vec[i][j].price;
        get_data( i+1 );
        tmp_price -= vec[i][j].price;
        
    }
}
int main()
{
    int a = 0;
    int n = 0;
    scanf( "%d", &a );
    scanf( "%d", &n ); 

    for( int i = 0; i < n; ++i )
    {
        scanf("%d",&a);
        vec.push_back( vector<product>() );
        for( int j = 0; j < a; ++j )
        {
            int b;
            vec[i].push_back( product() );
            scanf("%d", &b );
            vec[i][j].bandwidth = b;
            scanf("%d", &b );
            vec[i][j].price = b;

        }
    }

    for( int i = 0; i < vec.size(); ++i )
    {
        for( int j = 0; j < vec[i].size(); ++j )
        {

            cur_i = i;
            cur_j = j;
            tmp_price = vec[i][j].price;
            get_data( 0 );
        }
    }
    printf("%.03f", min_result);
}