#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
const int nmax=100000;
long long dp[nmax+5],a[nmax],b[nmax],k,n;
void bubblesort()
{
    int i,h,o;
    o=1;
    while(o==1)
    {
        o=0;
        for(i=1;i<=n-1;i++)
        {
            if(b[i]>b[i+1])
            {
               h=b[i];
               b[i]=b[i+1];
               b[i+1]=h;
               h=a[i];
               a[i]=a[i+1];
               a[i+1]=h;
               o=1;
            }
        }
    }

}
int main()
{
    int i,s,d;
    fin>>n;
    for(i=1; i<=n; i++)
    {
        fin>>a[i]>>b[i];
    }
    bubblesort();
    for(i=1;i<=n;i++)
    {
        s=i-1;
        d=b[i]-a[i];
        while(a[i]<b[s])
            s--;
        dp[i]=max(dp[i-1],dp[s]+d);
    }
    fout<<dp[n];
    return 0;
}