#include <cstdio>
#include <algorithm>

using namespace std;

#define MAX_N 100005
#define DIM 8192

int N, logN;
long A[MAX_N], B[MAX_N], Bst[MAX_N];
int P[MAX_N];
int Max;
char buf[DIM];
int pz;

void read(long &x)
{
    x = 0;
    while(!isdigit(buf[pz]))
        if(++pz == DIM)
            fread(buf, sizeof buf, DIM, stdin), pz = 0;
    while(isdigit(buf[pz]))
    {
        x = x*10 + (buf[pz] - '0');
        if(++pz == DIM)
            fread(buf, sizeof buf, DIM, stdin), pz = 0;
    }
}

void citire()
{
    long n;
    read(n);
    N = (int) n;

    for(int i = 1; i <= N; ++i)
    {
        read(A[i]); read(B[i]);
        P[i] = i;
    }
}

struct cmp
{
    bool operator()(const int a, const int b) const
    {
        return (B[a] < B[b]);
    }
};

int b_search(int x)
{
    int i, lg;
    for(i = 0, lg = logN; lg; lg >>= 1)
        if(i + lg <= N && B[P[i + lg]] <= x)
            i += lg;
    return i;
}

void solve()
{
    sort(P+1, P+N+1, cmp());

   /* for(logN = 1; logN <= N; logN <<= 1);

    for(int i = 1; i <= N; ++i)
    {
        Bst[i] = Bst[i-1];
        int poz = b_search(A[P[i]]);
        int dif = B[P[i]] - A[P[i]];
        if(dif + Bst[poz] > Bst[i])
            Bst[i] = dif + Bst[poz];
        if(Bst[i] > Max)
            Max = Bst[i];
    }
    printf("%d\n",Max);       */
}

int main()
{
    freopen("heavymetal.in","rt",stdin);
    freopen("heavymetal.out","wt",stdout);

    citire();
    solve();
}