#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;
vector <pair<int,int> > f;
int t[100005];
int n,a,b;
bool cmp(pair<int,int> la, pair<int,int> lb)
{
    return (la.first<lb.first) || (la.first==lb.first && la.second<lb.second);
}
int caut(int micv)
{
    int st=1,dr=n,m;
    while(st<dr)
    {
        m=(st+dr+1)/2;
        if(f[m].second<=micv)
            st=m;
        else
            dr=m-1;
    }
    return st;
}
int main()
{
    freopen("heavymetal.in","r",stdin);
    //freopen("heavymetal.out","w",stdout);
    f.push_back({0,0});
    scanf("%d",&n);
    for(int i=0;i<n;i++)
    {
        scanf("\n%d %d", &a,&b);
        f.push_back({a,b});
    }
    sort(f.begin()+1,f.end(),cmp);
    t[1]=f[1].second-f[1].first;
    for(int i=2;i<=n;i++)
        t[i]=max(t[i-1],t[caut(f[i].first)]+f[i].second-f[i].first);
    cout<<t[n];
    return 0;
}