#include<fstream>
#include<algorithm>
#define NMAX 100005
#define end first
#define begin second
using namespace std;
pair<int,int> v[NMAX];
int profit[NMAX],DP[NMAX],final[NMAX];
int n;
void read()
{
	ifstream fin("heavymetal.in");
	fin>>n;
	for(int i=1;i<=n;i++)
		fin>>v[i].begin>>v[i].end;
	fin.close();
}
void print()
{
	ofstream fout("heavymetal.out");
	fout<<DP[n];
	fout.close();
}
int binar(int v[],int s,int d,int val)
{
    if(s<=d)
    {
        int m=(s+d)/2;
        if(v[m]==val)
        {
            while(v[m+1]==val)
                m++;
            return m;
        }
        if(v[m]<val && v[m+1]>val)
            return m;
        if(v[m]>val && v[m-1]<val)
            return m-1;
        if(v[m]>val)
            return binar(v,s,m-1,val);
        return binar(v,m+1,d,val);
    }
	return 0;
}
int main()
{
	read();
	int i,poz;
	sort(v+1,v+n+1);
	for(i=1;i<=n;i++)
	{
		profit[i]=v[i].end-v[i].begin;
		final[i]=v[i].end;
	}
	DP[1]=profit[1];
	for(i=2;i<=n;i++)
	{
		poz=binar(final,1,i-1,v[i].begin);
		DP[i]=max(DP[i-1],DP[poz]+profit[i]);
	}
	print();
	return 0;
}