#include <stdio.h>
#include <algorithm>

using namespace std;

#define MAX_N 100005
#define FIN "heavymetal.in"
#define FOUT "heavymetal.out"
#define f first
#define s second
#define mp make_pair

int N, bst[MAX_N];
pair<int, int> A[MAX_N];

int main(void)
{
    int i, p;

    freopen(FIN, "r", stdin);
    freopen(FOUT, "w", stdout); 

    scanf("%d", &N);
    for (i = 0; i < N; ++i)
        scanf("%d %d", &A[i].s, &A[i].f);

    sort(A, A+N);
    for (i = 0; i < N; ++i)
    {
        bst[i] = A[i].f-A[i].s;
        if (i) bst[i] = max(bst[i], bst[i-1]);
        p = lower_bound(A, A+i, mp(A[i].s, A[i].s+1))-A;
        if (p) bst[i] = max(bst[i], bst[p-1]+A[i].f-A[i].s);
    }
    printf("%d\n", bst[N-1]);

    return 0;
}