#include <cstdio>
#include <algorithm>

using namespace std;

struct pair1
{
    int in,sf;
}nr[100001];

struct pair2
{
    int total,capat;
}v[100001];

char s[25];
int L;

bool cmp(const pair1 &a,const pair1 &b)
{
    return a.sf<b.sf;
}

int main()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    int n;
    scanf("%d ",&n);
    for (int i=1;i<=n;++i)
        scanf("%d %d\n",&nr[i].in,&nr[i].sf);
    sort(nr+1,nr+n+1,cmp);
    for (int i=1;i<=n;++i)
    {
        int j=0,step=1;
        for (;step<=L;step<<=1);
        for (;step;step>>=1)
            if (j+step<=L && v[j+step].capat<=nr[i].in)
            j+=step;
        if (v[j].total+(nr[i].sf-nr[i].in)>v[L].total)
        {
            ++L;
            v[L].capat=nr[i].sf;
            v[L].total=v[j].total+(nr[i].sf-nr[i].in);
        }
    }
    printf("%d",v[L].total);
}