#include <algorithm>
#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");

const int NMAX = 1e5;
pair<int, int> a[NMAX+5];
int dp[NMAX+5], n;

int Lower_bound(const int &value) {
    int left = 1, right = n, ans = 0;
    while (left <= right) {
        int middle = (left+right)/2;
        if (a[middle].second <= value)
            ans = middle, left = middle+1;
        else
            right = middle-1;
    }
    return ans;
}

bool cmp(const pair<int, int> &a, const pair<int, int> &b) {
    if (a.second == b.second)
        return a.first < b.first;
    return a.second < b.second;
}

int main() {
    ios_base :: sync_with_stdio(false);
    fin.tie(nullptr), fout.tie(nullptr);

    fin>>n;
    for (int i = 1; i <= n; i++)
        fin>>a[i].first>>a[i].second;
    sort(a+1, a+n+1, cmp);
    for (int i = 1; i <= n; i++) {
        int j = Lower_bound(a[i].first);
        dp[i] = max(dp[i-1], dp[j]+(a[i].second-a[i].first));
    }
    fout<<dp[n];
    return 0;
}