#include <cstdio>
#include <algorithm>

using namespace std;

struct INTERVAL
{
    int x,y;
};
INTERVAL v[100005];
bool cmp(INTERVAL a,INTERVAL b)
{
    if(a.x==b.x)
        return a.y>b.y;
    return a.x<b.x;
}
int main()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    int n,a,b,i,l,r,s;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d%d",&a,&b);
        v[i].x=a;
        v[i].y=b;
    }
    sort(v+1,v+n+1,cmp);
    l=v[1].x;
    r=v[1].y;
    s=r-l;
    for(i=2;i<=n;i++)
    {
        if(r<v[i].y)
        {
            if(v[i].x>=r)
            {
                s=s+v[i].y-v[i].x;
                l=v[i].x;
                r=v[i].y;
            }

        }
    }
    printf("%d",s);
    return 0;
}