#include<fstream>
#define DIM 10001
using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
int start[DIM], sfarsit[DIM];
int main()
{
    int i,j,o,n,aux,aux2,total,s,x;
    fin>>n;
    for(i=1;i<=n;++i)
    {
        fin>>start[i];

        fin>>sfarsit[i];
    }
    
    for(i=1;i<=n;++i)
         for(j=i+1;j<=n;++j)
              if((start[i]>start[j])||(start[i]==start[j]&&sfarsit[i]<sfarsit[j]))
                {
                    
                    aux=start[i];
                    aux2=sfarsit[i];
                    start[i]=start[j];
                    sfarsit[i]=sfarsit[j];
                    start[j]=aux;
                    sfarsit[j]=aux2;
                }
  
    total=0;
    x=0;
    s=0;
    for(i=1;i<=n;++i)
        if(start[i]>=x)
        {
            total=sfarsit[i]-start[i];
            x=sfarsit[i];
            s=s+total;
        }
    fout<<s;
    return 0;
}