#include <fstream>
#include <iostream>
#include <vector>
#include <bitset>
#include <string.h>
#include <algorithm>
#include <iomanip>
#include <math.h>
#include <time.h>
#include <stdlib.h>
#include <set>
#include <map>
#include <string>
#include <queue>
#include <deque>

using namespace std;

const char infile[] = "heavymetal.in";
const char outfile[] = "heavymetal.out";

ifstream fin(infile);
ofstream fout(outfile);

const int MAXN = 100005;
const int oo = 0x3f3f3f3f;

typedef vector<int> Graph[MAXN];
typedef vector<int> :: iterator It;

const inline int min(const int &a, const int &b) { if( a > b ) return b;   return a; }
const inline int max(const int &a, const int &b) { if( a < b ) return b;   return a; }
const inline void Get_min(int &a, const int b)    { if( a > b ) a = b; }
const inline void Get_max(int &a, const int b)    { if( a < b ) a = b; }

struct concert {
    int a, b;
};

struct classComp {
    inline bool operator () (const concert &a, const concert &b) const  {
        return a.b < b.b;
    }
};

concert heavy[MAXN];

int N, A[MAXN], B[MAXN], dp[MAXN];

inline int binarySearch(const int &st, const int &dr, const int &value) {
    int li = st, ls = dr;
    int Ans = -1;
    while(li <= ls) {
        int mid = ((li + ls) >> 1);
        if(heavy[mid].b <= value) {
            Ans = mid;
            li = mid + 1;
        }
        else ls = mid - 1;
    }
    return Ans;
}

int main() {
    fin >> N;
    for(int i = 1 ; i <= N ; ++ i)
        fin >> heavy[i].a >> heavy[i].b;
    sort(heavy + 1, heavy + N + 1, classComp());
    for(int i = 1 ; i <= N ; ++ i) {
        int bestpos = binarySearch(1, i, heavy[i].a);
        dp[i] = dp[i-1];
        if(bestpos != -1)
            dp[i] = max(dp[i], dp[bestpos] + heavy[i].b - heavy[i].a);
        else dp[i] = max(dp[i], heavy[i].b - heavy[i].a);
    }
    fout << dp[N] << '\n';
    fin.close();
    fout.close();
    return 0;
}