#include <fstream>
#include <algorithm>
using namespace std;
const int nmax=100005;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
struct interval
{
    int x,y;
}v[nmax];
bool cmp(interval a,interval b)
{
    return a.y<b.y;
}
int cautbin (int tinta,int st,int dr)
{
    int ans=0;
    while (st<=dr)
    {
        int mij=(st+dr)/2;
        if (v[mij].y<=tinta)
        {
            ans=mij;
            st=mij+1;
        }
        else
            dr=mij-1;
    }
    return ans;
}
int main()
{
    int n,dp[nmax];
    f>> n;
    for (int i=1;i<=n;i++)
    {
        f>> v[i].x >> v[i].y;
    }
    sort (v+1,v+n+1,cmp);
    dp[1]=v[1].y-v[1].x;
    for (int i=2;i<=n;i++)
    {
        int j=cautbin(v[i].x,1,i-1);
        dp[i]=max(dp[i-1],dp[j]+v[i].y-v[i].x);
    }
    g<< dp[n];
}