#include <bits/stdc++.h>

using namespace std;

const int nmax = 100000;

struct concert
{
    int s,f;
}v[1+nmax];

int sf[1+nmax];
long long dp[1+nmax];

bool cmp(concert a,concert b)
{
    return a.f < b.f;
}

int m;

int caut(int x)
{
    int r = 0,pas = 1 << 16;
    while(pas)
    {
        if((r+pas) <= m && x >= sf[r+pas])
            r += pas;
        pas /= 2;
    }
    return r;
}

int main()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    int n;
    cin >> n;
    for(int i = 1;i <= n;i ++)
        cin >> v[i].s >> v[i].f;
    sort(v+1,v+n+1,cmp);
    for(int i = 1;i <= n;i ++)
    {
        if(v[i].f != v[i-1].f)
            sf[++m] = v[i].f;
    }
    int dr = 0;
    for(int i = 1;i <= n;i ++)
    {
        int st = caut(v[i].s);
        if(v[i].f > sf[dr])
            dr ++;
        dp[dr] = max(dp[dr], dp[st] + 1LL*(v[i].f - v[i].s));
        dp[dr] = max(dp[dr],dp[dr-1]);
    }
    cout << dp[m];
    return 0;
}