#include<bits/stdc++.h>
#define endl '\n';
using namespace std;
int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int n,a,b,p=1,ans=0;
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a>>b;
		if(abs(b-p)>abs(a-p)){
			ans+=abs(b-p);
			p=b;
		}else{
			ans+=abs(a-p);
			p=a;
		}//cerr<<ans<<" "<<p<<"\n"<<endl;
	}cout<<n-p+ans+n-1;
	return 0;
}