#include <cstdio>
#include <algorithm>
#define maxN 100005
using namespace std;
//in dp[i] pastrez maximul timpului de concert pana la intervalul i
int n, i, st, dr, m, poz, dp[maxN];
long long sum;
struct trupa
{
    int x, y;
}v[maxN];
bool cmp(trupa a, trupa b)
{
    return a.y < b.y;
}
int main()
{
    freopen("heavymetal.in", "r", stdin);
    freopen("heavymetal.out", "w", stdout);
    scanf("%d", &n);
    for(i = 1; i <= n; i++)
        scanf("%d %d\n", &v[i].x, &v[i].y);
    sort(v+1, v+n+1, cmp);
    //cayt upper_bound pentru capatul a de interval
    for(i = 1; i <= n; i++)
    {
        st = 1, dr = i-1;
        while(st<=dr)
        {
            m = (st+dr)>>1;
            if(v[m].y <= v[i].x) poz = m, st = m+1;
            else dr = m-1;
        }
        dp[i]=max(dp[i-1], dp[poz] + v[i].y - v[i].x);
    }
    printf("%d", dp[n]);
    return 0;
}