#include<stdio.h>   
#include<algorithm>   
#include<cstdlib>   
#define dim 100001   
using namespace std;   
  
int Be[dim], A[dim], B[dim];   
int V[dim];   
  
int max(int a, int b)   
{   
    //if(a > b) return a;   
    return a > b ? a : b;   
}   
  
  
void qsort(int inc, int sf)   
{   
    int i,j,temp, aux;   
    i = inc;   
    j = sf;   
    temp = B[V[rand()%(j-i)+i]];   
       
    do  
      { while(B[V[i]] < temp) i++;   
        while(B[V[j]] > temp) j--;   
          if(i < j) aux = V[i], V[i] = V[j], V[j] = aux;   
          if(i <= j) j--, i++;   
      } while (i <= j);   
  
    if(inc < j) qsort(inc, j);   
    if (i < sf) qsort(i, sf);   
}   
  
    
int main()   
{ int T;   
  int i,j,k,N,t;   
  
      FILE *f = fopen("heavymetal.in", "r");   
      FILE *g = fopen("heavymetal.out", "w");   
         
      fscanf(f, "%d", &N);   
         
      for(i = 1; i <= N; i++)   
          {   
              fscanf(f, "%d%d", &A[i], &B[i]);   
              V[i] = i;   
          }   
         
      qsort(1, N);   
         
      T = B[V[N]];   
         
      k = 1;   
      for(i = 1; i <= N; i++)   
          {   
              for(t = k+1; t <= B[V[i]]; t++)   
                  Be[t] = Be[t-1];   
              //while(B[V[k]] < i) k++;   
              //if(B[V[k]] == i)   
                  //{   
                      //Be[i] = Be[i-1];   
                      for(j = 1; j <= N; j++)   
                         if(B[V[j]] == B[V[i]])   
                            Be[B[V[i]]] = max(Be[B[V[i]]], Be[A[V[j]]] + (B[V[j]] - A[V[j]]));  
							 else if(B[V[j]] > B[V[i]]) break;
                 //}   
                k = B[V[i]];   
          }   
         
      fprintf(g, "%d\n", Be[T]);   
         
         
      fclose(f);   
      fclose(g);   
      return 0;   
}