#include <fstream>
#include <algorithm>

using namespace std;

ifstream f("heavymetal.in");
ofstream g("heavymetal.out");

struct concerte
{
    int x,y;
} v[100001];
bool comp(concerte a, concerte b)
{
    return (a.y<b.y)||(a.y==b.y&&a.x>b.x);
}
long long n,i,j,smax,s[100001];

int main()
{
    f>>n;
    for(i=1; i<=n; i++)
    {
        f>>v[i].x>>v[i].y;
    }
    sort(v+1,v+n+1,comp);
    i=1;
    for(j=1;j<=v[n].y;j++){
        s[j]=s[j-1];
        while(v[i].y==j){
            s[j]=max(s[j],s[v[i].x]+v[i].y-v[i].x);
            i++;
        }
    }
    g<<s[v[n].y];
    return 0;
}