#include <fstream>
#include <algorithm>

using namespace std;

const int NMAX=100001;
int n, i, l, r, pos, d[NMAX];

struct sp
{
    int a, b;
} v[NMAX];

inline bool cmp(sp x, sp y)
{
    return x.b<y.b;
}

int main()
{
    ifstream fin("heavymetal.in");
    ofstream fout("heavymetal.out");
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i].a>>v[i].b;
    sort(v+1,v+n+1,cmp);
    for(i=1;i<=n;i++)
    {
        l=1;
        r=i-1;
        pos=0;
        while(l<=r)
        {
            int mid=(l+r)/2;
            if(v[mid].b<=v[i].a)
            {
                l=mid+1;
                pos=mid;
            }
            else
                r=mid-1;
        }
        d[i]=max(d[i-1],d[pos]+v[i].b-v[i].a);
    }
    fout<<d[n]<<'\n';
    return 0;
}