#include <stdio.h>
#include <stdlib.h>
#define max(a,b)((a>b)?a:b)
#define FOR(i,s,d) for(i=(s);i<=(d);++i)
long a[100005],b[100005],n,i,j,v[1000001],ind[1000001],x[100005],q,s,d,mid;

int comp(const void * n1 ,const void * n2){
    return b[*((long*)n1)]-b[*((long*)n2)];
}

int main ()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    scanf("%ld",&n);
    FOR (i,1,n){
        scanf("%ld %ld",&a[i],&b[i]);
        ind[i]=i;
        }
    qsort(ind+1,n,sizeof(long),comp);

    FOR (i,1,n){
        if (x[q]!=b[i])q++;
        x[q]=b[ind[i]];
        v[q]=v[q-1];
        s=1;d=q;
        while (s<d)   
              {
              long mid=(s+d)/2;
              if (x[mid]>a[ind[i]])
                 d=mid;
                 else 
                 s=mid+1;
              }
        if(s<q&&x[s]==a[ind[i]])
        v[q]=max(v[q],v[s]+b[ind[i]]-a[ind[i]]);
        else
        v[q]=max(v[q],v[s-1]+b[ind[i]]-a[ind[i]]);
        }
    printf("%ld",v[q]);
    //printf("\n");
    //FOR (i,1,q)printf("%ld ",v[i]);
    return 0;   
}