#include <bits/stdc++.h>

using namespace std;

const int NMAX = 100003;

int n;

struct elem {
    int x, y;
} v[NMAX];

bool cmp(elem a, elem b) {
    return a.y < b.y;
}

int main() {
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) {
        scanf("%d %d", &v[i].x, &v[i].y);
    }
    sort(v + 1, v + n + 1, cmp);
    int st = v[1].x, dr = v[1].y, hmax = v[1].y - v[1].x;
    int ans = 0;
    for (int i = 2; i <= n; i++) {
        if(dr <= v[i].x || v[i].y <= st){
            ans += hmax;
            st = v[i].x;
            dr = v[i].y;
            hmax = v[i].y - v[i].x;
        }else{
            if(hmax < v[i].y - v[i].x ){
                hmax = v[i].y - v[i].x;
                st = v[i].x;
                dr = v[i].y;
            }
        }
    }
    ans += dr-st;
    printf("%d\n",ans);

    return 0;
}