#include <cstdio>
#include <algorithm>
using namespace std;
struct spec
{
    int x,y;
};
bool cmp(spec a,spec b)
{
    if(a.x==b.x)return a.y<b.y;
    return a.x<b.x;
}
spec v[1000005];
int main()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    int n,i;
    scanf("%d",&n);
    for(i=1;i<=n;i++)scanf("%d %d",&v[i].x,&v[i].y);
    sort(v+1,v+n+1,cmp);
    int sum=0,ant=0;
    for(i=1;i<=n;i++)
    {
        if(v[i].x>=ant)
        {while(v[i].x==v[i+1].x)i++;
        sum+=v[i].y-v[i].x;
        ant=v[i].y;
    }
    }
    printf("%d\n",sum);
    return 0;
}