#include <iostream>
#include <fstream>
using namespace std;
int n,i,j,sf[100005],inc[100005],aux,s;
ifstream in("heavymetal.in");
ofstream out("heavymetal.out");
void citire()
{
    in>>n;
    for (i=1;i<=n;i++) in>>inc[i]>>sf[i];
}
void ordonare()
{
    for (i=1;i<n;i++)
        for (j=i+1;j<=n;j++)
        if (sf[i]>sf[j])
    {
        aux=sf[i];sf[i]=sf[j];sf[j]=aux;
        aux=inc[i];inc[i]=inc[j];inc[j]=aux;
    }
}
void rezolvare()
{
    int ultim;
    for (ultim=0,i=1;i<=n;i++)
        if (inc[i]>=sf[ultim])
    {
        while (inc[i+1]==inc[i]) i++;
        s=s+sf[i]-inc[i];
        ultim=i;
    }
}
int main()
{
    citire();
    ordonare();
    rezolvare();
    out<<s;
}