#include <bits/stdc++.h>
using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
int dp[1<<17];
vector<int> v[1<<17];

int main()
{
    int n;
    fin >> n;
    int maxDr = 0;
    while(n--)
    {
        int st, dr;
        fin >> st >> dr;
        v[dr].push_back(st);
        maxDr = max(maxDr, dr);
    }
    for(int i = 1;i <= maxDr; ++i) {
        dp[i] = dp[i - 1];
        for(auto st : v[i]) {
            dp[i] = max(dp[i], dp[st] + i - st);
        }
    }
    fout << dp[maxDr];
    return 0;
}