#include <bits/stdc++.h>
#define pb push_back

using namespace std;

ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");

void debug_out() { cerr << '\n'; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) { cerr << " " << H; debug_out(T...);}
#define dbg(...) cerr << #__VA_ARGS__ << " ->", debug_out(__VA_ARGS__)
#define dbg_v(x, n) do{cerr<<#x"[]: ";for(int _=0;_<n;++_)cerr<<x[_]<<" ";cerr<<'\n';}while(0)
#define dbg_ok cerr<<"OK!\n"

typedef pair<int,int> pii;
typedef long long int ll;
typedef long double ld;

class aib{
    private:
        int n;
        vector <int> tree;

    public:
        aib(int n){
            this->n=n;
            tree.resize(n+1);
        }
        void update(int x,int quantity){
            int i;
            for(i=x;i<=n;i+= ((i)&(-i)))
                tree[i]=max(tree[i],quantity);
        }
        int query(int x){
            int i,ans=0;
            for(i=x;i>0;i-= ((i)&(-i)))
                ans=max(tree[i],ans);
            return ans;
        }
};

const int DMAX = 2e5+10;

vector <int> vec;
int pos[DMAX];

pii V[DMAX];

int n;
int dif;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int t,i,j;
    int poz,poz2,maxim;

    fin>>n;
    for(i=1;i<=n;i++){
        fin>>V[i].first>>V[i].second;
        vec.pb(V[i].first);
        vec.pb(V[i].second);
    }
    sort(V+1,V+n+1);
    sort(vec.begin(),vec.end());
    dif=1;
    pos[0]=1;
    for(i=1;i<vec.size();i++)
        if(vec[i] != vec[i-1])
            pos[i]=++dif;
        else
            pos[i]=dif;
    aib tree(dif);
    for(i=1;i<=n;i++){
        poz=lower_bound(vec.begin(),vec.end(),V[i].first)-vec.begin();
        poz2=lower_bound(vec.begin(),vec.end(),V[i].second)-vec.begin();
        maxim=tree.query(pos[poz]);
        tree.update(pos[poz2],maxim+V[i].second-V[i].first);
    }
    fout<<tree.query(dif)<<'\n';
    return 0;
}