#include <bits/stdc++.h>

using namespace std;

const int N = 1e5;

int dp[5 + N];
int Max[5 + N];
pair <int,int> spec[5 + N];

bool cmp(pair <int,int> a, pair <int,int> b){
    return a.second < b.second;
}

int cautbin(int n, int dr){
    int r, pas;
    r = 0;
    pas = 1 << 20;
    while(pas){
        if(r + pas <= n && spec[r + pas].second <= dr)
            r += pas;
        pas >>= 1;
    }
    return r;
}

int main()
{
    freopen("heavymetal.in", "r", stdin);
    freopen("heavymetal.out", "w", stdout);
    int n;
    scanf("%d", &n);
    for(int i = 1; i <= n; i++)
        scanf("%d%d", &spec[i].first, &spec[i].second);
    sort(spec + 1, spec + n + 1, cmp);

    for(int i = 1; i <= n; i++){
        int st, dr, pos;
        st = spec[i].first;
        dr = spec[i].second;
        pos = cautbin(i, st);
        dp[i] = dr - st + Max[pos];
        Max[i] = max(Max[i - 1], dp[i]);
    }

    printf("%d\n", Max[n]);
    return 0;
}