#include <bits/stdc++.h>
using namespace std;
ifstream f ("heavymetal.in");
ofstream g ("heavymetal.out");
int n,m,i,j,nr,sf,sum;
struct spec
{
    int x,y;
} v[100001],ax;

int main()
{
    f>>n;
    for(i=1; i<=n; i++) f>>v[i].x>>v[i].y;
    for(i=1; i<=n; i++)
        for(j=i+1; j<=n; j++)
            if(v[i].y>v[j].y)
                ax=v[i],v[i]=v[j],v[j]=ax;

    nr=1;
    sum+=(v[1].y-v[1].x)+1;
    sf=v[1].y;
    for(i=2; i<=n; i++)
    {
        if(v[i].x>=sf)
        {
            nr++;
            //cout<<v[i].x<<" "<<v[i].y<<endl;
            sum+=(v[i].y-v[i].x);
            sf=v[i].y;
        }
    }
    g<<sum;

    return 0;
}