#include <fstream>
#include <algorithm>

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

int n,i,sol;
long long d[100001];
struct numar{
    int x,y;
}v[100001];

int cmp(numar a, numar b){
    if(a.y==b.y)
        return a.x<b.x;
    return a.y<b.y;
}

int cautbin(long long k,int dr){
    int st=1,sol=0,mij;
    while(st<=dr){
        mij=(st+dr)/2;
        if(v[mij].y<=k){
            sol=mij;
            st=mij+1;
        }
        else
            dr=mij-1;
    }
    return sol;
}

int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i].x>>v[i].y;
    sort(v+1,v+n+1,cmp);
    d[1]=v[1].y-v[1].x;
    for(i=2;i<=n;i++){
        sol=cautbin(v[i].x,i-1);
        d[i]=max(d[i-1],d[sol]+v[i].y-v[i].x);
    }
    fout<<d[n];
    return 0;
}