#include<cstdio>
#include<algorithm>
using namespace std;
const int NMAX=100000;
struct SEGM
{
    int x, y;
};
SEGM s[NMAX+5];
int d[NMAX+5];
bool cmp(const SEGM &a, const SEGM &b)
{
    return a.y<b.y;
}
int bs(int st, int dr, int val)
{
    int med, last=-1;
    while(st<=dr)
    {
        med=(st+dr)>>1;
        if(s[med].y<=val)
            last=med, st=med+1;
        else
            dr=med-1;
    }
    return last;
}
int main()
{
    FILE *in, *out;
    in=fopen("heavymetal.in", "r");
    out=fopen("heavymetal.out", "w");
    int i, n, x, y, j;
    fscanf(in, "%d", &n);
    for(i=1; i<=n; ++i)
    {
        fscanf(in, "%d%d", &x, &y);
        s[i].x=x;
        s[i].y=y;
    }
    fclose(in);
    sort(s+1, s+n+1, cmp);
    for(i=1; i<=n; ++i)
    {
        d[i]=d[i-1];
        j=bs(1, i-1, s[i].x);
        if(j==-1)
        {
            if(d[i]<s[i].y-s[i].x)
                d[i]=s[i].y-s[i].x;
        }
        else
            if(d[i]<d[j]+s[i].y-s[i].x)
                d[i]=d[j]+s[i].y-s[i].x;
    }
    fprintf(out, "%d", d[n]);
    fclose(out);
}