#include<stdio.h>
#include<algorithm>
using namespace std;
inline long max(long c,long b)
{
    if(b>=c)
        return b;
    return c;
}   
struct casy
{
long x,y;
};
casy a[100011];
long cost[100011];
long cb(long dr,long c)
{
long last=0,st,m;   
st=1;
while(st<=dr)
{
m=(st+dr)>>1;
if(a[m].y<=c)
{
    last=m;
    st=m+1;
}
else
    dr=m-1;
}
return last;
}
int comp(const void *c,const void *b)
{
    casy *pc,*pb;
    pc=(casy*)c;
    pb=(casy*)b;
    if(pc->y>pb->y)
        return 1;
    if(pc->y==pb->y)
        return 0;
    return -1;
}   
bool comp2(casy a,casy b)
{
    return a.y<b.y;
}   
int main()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    long n,i;
    scanf("%ld",&n);
    for(i=1;i<=n;i++)
        scanf("%ld%ld",&a[i].x,&a[i].y);
    //qsort(a+1,n,sizeof(a[0]),comp);
    sort(a+1,a+n+1,comp2);
    cost[1]=a[1].y-a[1].x;
    for(i=2;i<=n;i++)
        cost[i]=max(cost[i-1],a[i].y-a[i].x+cost[cb(i-1,a[i].x)]);
    printf("%ld\n",cost[n]);
    return 0;
}