#include<cstdio>
#include<algorithm>
using namespace std;
struct data{
    int x;
    int y;
    int z;
    bool operator <(const data &oth) const
    {
        if(x<oth.x) return 1;
        if(x>oth.x) return 0;
        return y<oth.y;
    }
}cow[100003];
int ef(int a,int b,int t)
{    if(a==b) {
      if(cow[a].x>t)
      return a;  
      return 0;
      }               
     int mid=a+(b-a)/2;
     if(cow[mid].x<=t) return ef(mid+1,b,t);
     else return ef(a,mid,t);
}
int f[100004];
int main()

{  
    int b;
   scanf("%d",&b);
   for(int i=1;i<=b;i++)
   {
    scanf("%d%d",&cow[i].x,&cow[i].y);
    cow[i].z=cow[i].y-cow[i].x+1;
   }
   sort(cow+1,cow+1+b);
   f[b]=cow[b].z;
   for(int i=b-1;i>=1;i--)
    f[i]=max(f[i+1],f[ef(i+1,b,cow[i].y)]+cow[i].z);
   printf("%d",f[1]);
    return 0;
}