#include <iostream>
#include <stdio.h>
#include <vector>
#include <algorithm>

using namespace std;

FILE *f, *g;

struct concert{
  int A, B;
};

int N, A, B;
int Tmax;
vector<concert> C;
vector<int> Best;

concert Make(int A, int B)
{
  concert r = {A, B};
  return r;
}

bool How(concert c1, concert c2)
{
  return c1.B < c2.B;
}

int main()
{
  f = fopen ("heavymetal.in", "r");
  g = fopen ("heavymetal.out", "w");

  fscanf(f, "%d", &N);
  for (int i = 1; i <= N; i++)
  {
    fscanf(f, "%d %d", &A, &B);
    C.push_back(Make(A, B));
    Tmax = max(Tmax, B);
  }

  //Sortez crescator dupa campul B.
  sort(C.begin(), C.end(), How);

  //for (int i = 0; i < N; i++) cout << C[i].A << " " << C[i].B << endl;

  Best.push_back(0);
  for (int i = 1; i <= Tmax; i++)
  {
    Best.push_back(Best[i-1]);
    for (int j = 0; j < N; j++)
    {
      if (C[j].B == i) Best[i] = max(Best[i], Best[C[j].A] + (C[j].B - C[j].A));
      else if (C[j].B > i) break;
    }
  }

  fprintf(g, "%d", Best[Tmax]);

  fclose (f);
  fclose (g);

  return 0;
}