#include<bits/stdc++.h>
using namespace std;
#define ll long long
ll a[20005];
ll b[20005];
ll c[40005];
ll f[40005];
int main(){
	ll n;
	cin>>n;
	ll ans=0,k=1;
	for(int i=1;i<=n;i++){
		cin>>a[i]>>b[i];
		c[k++]=a[i];
		c[k++]=b[i];
	}
	sort(c+1,c+1+2*n);
	for(int i=1;i<=n;i++){
		a[i]=lower_bound(c+1,c+1+2*n,a[i])-c;
		b[i]=upper_bound(c+1,c+1+2*n,b[i])-c;
		for(int j=a[i];j<b[i];j++){
			f[j]=1;
		}
	}
	for(int i=1;i<2*n;i++){
		if(f[i]) ans+=c[i+1]-c[i];
	}
	cout<<ans<<endl;
	return 0;
}