#include <fstream>
#include <algorithm>
using namespace std;
ifstream fi("heavymetal.in");
ofstream fo("heavymetal.out");

struct spectacol
{
    int a,b;
};

bool operator<(const spectacol &x,const spectacol &y)
{
    return x.b<y.b;
}

int dp[100005];
spectacol S[100005];
int n;
int main()
{
    fi>>n;
    for (int i=1; i<=n; i++)
        fi>>S[i].a>>S[i].b;
    sort(S+1,S+n+1);
    for (int i=1; i<=n; i++)
    {
        int st=0,dr=i-1;
        while (st<dr)
        {
            int mij=(st+dr+1)/2;
            if (S[mij].b<=S[i].a)
                st=mij;
            else
                dr=mij-1;
        }
        dp[i]=max(dp[i-1],dp[st]+S[i].b-S[i].a);
    }
    fo<<dp[n];
    fi.close();
    fo.close();
    return 0;
}