#include <fstream>
#include <algorithm>

using namespace std;
struct bg
{
    int x,y;
}v[100003];

int d[1000003];

bool cmp(bg a, bg b)
{
    return a.y < b.y;
}

int main()
{
    ifstream in("heavymetal.in");
    ofstream out("heavymetal.out");
    int l, n, i;
    l= 1;
    in >> n;
    for(i=1;i<=n;i++)  in >> v[i].x >> v[i].y;
    sort(v+1,v+n+1,cmp);
    for(i=1;i<=v[n].y;i++)
    {
        d[i]=d[i-1];
        while(v[l].y==i)
        {
           d[i]=max(d[i],d[v[l].x]+i-v[l].x);
            l++;
        }
    }
    out << d[ v[n].y ] << '\n';
    return 0;
}