#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=2e4+10;
int n;
int b[N],a[N];
int x[N<<1],ans;
bool v[N<<1];
signed main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i]>>b[i];
		x[i]=a[i];
		x[i+n]=b[i];
	}
	sort(x+1,x+2*n+1);
	for(int i=1;i<=n;i++){
		int start=lower_bound(x+1,x+2*n+1,a[i])-x;
		int end=lower_bound(x+1,x+2*n+1,b[i])-x;
		for(int j=start;j<end;j++){
		v[j]=1;
		}
	}
	for(int i=1;i<2*n;i++)
	if(v[i])
	ans+=x[i+1]-x[i];
	cout<<ans; 
	return 0;
}
//龙卷风