#include <fstream>
#include <algorithm>
#define LIM 16

using namespace std;

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

long long dp[100001], f[100001];
int n, m;
pair <long long, long long> v[100001];

int cautbin(int x) {
    int r = 0, pas = 1 << LIM;
    while (pas != 0) {
        if (r + pas <= m && f[r + pas] <= x) {
            r += pas;
        }
        pas >>= 1;
    }
    return r;
}

int main()
{
    in >> n;
    for (int i = 1; i <= n; i++) {
        in >> v[i].second >> v[i].first;
        f[i] = v[i].first;
    }
    sort(v + 1, v + n + 1);
    sort(f + 1, f + n + 1);
    for (int i = 2, j = 1; i <= n; i++) {
        if (f[i] != f[i - 1]) f[++j] = f[i];
        m = j;
    }

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