/*
ID: xxxxx
TASK: speeding
LANG: C++
*/
#include <vector>
#include <iostream>
#include <fstream>
#include <algorithm>

std::ifstream infile("speeding.in");
std::ofstream outfile("speeding.out");

int main() {
  int example, bessie;

  infile >> example >> bessie;

  int exampleList[example];
  int exampleSpeeding[example];

  int bessieList[bessie];
  int bessieSpeedProjected[example];

  for (int i = 0; i < example; i++)
    infile >> exampleList[i] >> exampleSpeeding[i];
  for (int i = 0; i < bessie; i++)
    infile >> bessieList[i] >> bessieSpeedProjected[i];

  int currentTravelTime[100];
  int currentSpeedLimit[100];
  int mile = 0;

  for (int i = 0; i < example; i++){
    for(int j = 0; j < exampleList[i]; j++){
      currentSpeedLimit[mile] = exampleSpeeding[i];
      mile++;
    }
  }
  int bessieTravelTime[100];
  int bessieSpeed[100];
  mile = 0;

  for (int i = 0; i < bessie; i++){
    for(int j = 0; j < bessieList[i]; j++){
      bessieSpeed[mile] = bessieSpeedProjected[i];
      mile++;
    }
  }
  int amountOver = 0;
  for (int i = 0; i < 100; i++){
    int numba = bessieSpeed[i] - currentSpeedLimit[i];
    if (numba > amountOver)
      amountOver = numba;
  }

  outfile << amountOver;
}