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#pragma warning (disable : 4996)
#pragma comment(linker, "/STACK:36777216")



#include <stdlib.h>
#include <iostream>
#include <vector>
#include <string>
#include <assert.h>
#include <stack>
#include <algorithm>
#include <ios>
#include <iostream>
#include <fstream>
#include <iomanip>
#include <queue>
#include <set>
#include <functional>
#include <cmath>
#include <sstream>
#include <map>
#include <memory.h>
#include <stdio.h>
#include <cassert>
#include <string.h>
#include <deque>
#include <ctime>
#include <unordered_map>
#include <list>

#define forn(i , n) for (i64 i = 0; i < n; ++i)
#define down(i, n) for (int i = (n) - 1; i >= 0; --i)


using namespace std;

typedef unsigned long long int u64;
typedef long long int i64;
typedef vector<int> vint;
typedef vector<i64> vi64;
typedef pair<int, int> pint;
typedef pair<i64, i64> pi64;

#define FILE_NAME "file"
#define CONTEST "seq"
#define M_PI 3.14159265358979323846
#define ALL(a) (a).begin(), (a).end()


const int inf = 1000000000;

#define MOD 1000000007


#define EPS 10E-10

const int N = 2000000;


struct Event
{
    int a, o, i;
    bool operator<(const Event & b) const
    {
        return a < b.a;
    }
};


int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout << fixed << setprecision(15);
    srand(16);
    int start = clock();
#ifdef FILE_INPUT
    freopen(FILE_NAME ".in", "r", stdin);
    freopen(FILE_NAME ".out", "w", stdout);
#endif

    int n;
    cin >> n;
    vector<pint> arr(n);
    vector<Event> events;
    forn(i, n)
    {
        cin >> arr[i].first >> arr[i].second;
        Event a;
        a.a = arr[i].first;
        a.i = i;
        a.o = 0;
        events.push_back(a);
        a.a = arr[i].second;
        a.o = 1;
        events.push_back(a);
    }
    sort(events.begin(), events.end());
    int l = 0, r = 10000 / n + 1;
    while (r - l > 1)
    {
        int m = (r + l) / 2;
        vector<int> want(n, m);
        set<int> available;
        vector<int> will(n, 0);
        int currE = 0;
        forn(i, 10001)
        {
            while (currE < events.size() && i >= events[currE].a)
            {
                int j = events[currE].i;
                if (events[currE].o == 0)
                {
                    available.insert(j);

                    will[j] = arr[j].second - arr[j].first;
                }
                else
                {
                    available.erase(j);
                }
                currE++;
            }
            int bestToEat = -1;
            int res = -1000000000;
            for (auto & j : available)
            {
                int c = want[j] - will[j];
                if (want[j] && c > res)
                {
                    bestToEat = j;
                    res = c;
                }
                will[j]--;
            }
            if (bestToEat != -1)
            {
                want[bestToEat]--;
            }
        }
        bool bad = false;
        forn(i, n)
        {
            if (want[i] > 0)
            {
                r = m;
                bad = true;
                break;
            }
        }
        if (!bad)
        {
            l = m;
        }
    }


    cout << l * n;
    return 0;
}