#include <fstream>
#include <algorithm>
#include <cmath>

using namespace std;
ifstream in ("heavmetal.in");
ofstream out ("heavymetal.out");
struct vagos
{
    int x;
    int y;
} v[1000];
int compare (vagos a,vagos b)
{
    return(a.y<b.y);
}
int main()
{
    int n,i,s,a;
    in>>n;
    for(i=1; i<=n; i++)
    {
        in>>v[i].x>>v[i].y;

    }
    sort(v+1,v+n+1,compare);
    s=0;
    for(i=1; i<=n; i++)
    {
        a=v[i].y;
        while(a>v[i].x)i++;
        s+=v[i].y-v[i].x;
        i--;
    }
    out<<abs(s);
    return 0;
}