#include <bits/stdc++.h>

using namespace std;
struct show
{
    int x,y;
};
show v[100005];
bool cmp(show a,show b)
{
    if(a.x < b.x)
        return 1;
    else if(a.x == b.x)
        if(a.y > b.y)
            return 1;
    return 0;
}
int main()
{
    freopen("heavymetal.in", "r",stdin);
    freopen("heavymetal.out", "w",stdout);
    int n,a,b,s = 0,x,y;
    scanf("%d", &n);
    for(int i = 1;i <= n;i++)
        scanf("%d %d", &v[i].x, &v[i].y);
    sort(v + 1,v + n + 1,cmp);
    x = v[1].x;
    y = v[1].y;
    s += y - x;
    for(int i = 2;i <= n;i++)
    {
        if(v[i].x >= y)
        {
            x = v[i].x;
            y = v[i].y;
            s += y - x;
        }
    }
    printf("%d",s);
    return 0;
}