#include <bits/stdc++.h>

using namespace std;

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

int n, a[100005], b[100005], dp[1005][1005] ;

struct idk
{
    int a, b;
}v[100005];

int solve(int index, int last)
{
    if (dp[index][last] > 0) return dp[index][last];
    if (index > n) return 0;
    if (v[index].a >= last)
        return dp[index][last] = max(solve(index + 1, last), v[index].b - v[index].a + solve(index + 1, v[index].b));
    return dp[index][last] = solve(index + 1, last);
}

bool cmp(idk aa, idk bb)
{
    return aa.a < bb.a;
}

int main()
{
    fin >> n;
    for (int i = 1; i <= n; ++i)
    {
        fin >> v[i].a >> v[i].b;
    }
    sort(v + 1, v + n + 1, cmp);
    fout << solve(1, 0);
    return 0;
}