#include <bits/stdc++.h>
#define pii pair<int, int>
#define pb push_back
#define mp make_pair
#define NMAX 100013
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
int N, K, target;
int w, m;
vector <pii> Bands;
int dp[NMAX];

int bsrch(int left, int right, int x) {
    int mid, sol = -1;
    while (left <= right) {
        mid = (left + right) / 2;
        if (Bands[mid].second <= x) {
            left = mid + 1;
            sol = mid;
        }
        else right = mid - 1;
    }
    if (sol >= 0) return dp[sol];
    return 0;
}
int main() {
    f >> N;
    for (int i = 0; i < N; ++i) {
        pii pe;
        cin >> pe.second >> pe.first;
        Bands.pb(pe);
    }
    sort(Bands.begin(), Bands.end());
    for (int i = 0; i < N; ++i) {
        swap (Bands[i].first, Bands[i].second);
    }
    dp[0] = Bands[0].second - Bands[0].first;
    for (int i = 1; i < N; ++i) {
        dp[i] = max(dp[i - 1], Bands[i].second - Bands[i].first + bsrch(0, i, Bands[i].first));
    }
    g << dp[N - 1];
    return 0;
}