#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;
long int a[20000], b[20000];
void qs(int l, int r){
    int x=a[l+(r-l)/2];
    int i=l;
    int j=r;
    while (i<=j){
        while (a[i]<x) i++;
        while (a[j]>x) j--;
        if(i<=j){
            swap(a[i],a[j]);
            swap(b[i],b[j]);
            i++;
            j--;
        }
    }
    if(i<r) qs(i,r);
    if(l<j) qs(l,j);
}
int main(){
    int i,n;
    int max,min,sum;
    cin >>n;
    for(i=1;i<=n; i++){
        cin >>a[i] >>b[i];
    }
    qs(1,n);
    min=a[1];
    max=b[1];
    sum=0;
    for(i=2;i<=n;i++){
        if(b[i]>max && a[i]<=max) max=b[i];
        if(a[i]>max) {sum=sum+max-min; min=a[i]; max=b[i];}
    }
    sum=sum+max-min;
    cout <<sum;
    return 0;
}