#include<bits/stdc++.h>
using namespace std;
int n;
long long t[100005],a[100005],sum;
int main(){
	freopen("a.in","r",stdin);
	freopen("a.out","w",stdout);
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>t[i]>>a[i];
	}
	int lastt=n,lasta=n;
	for(int i=n-1;i>=1;i--){
		if(a[i]>a[lasta]){
			lasta=i;
			long long e1=a[i]*2+t[i]-t[lastt],e2=(a[i]-a[lasta])*2;
			if(e1<=0){
				lastt=i;
				continue ;
			} 
			else if(e1<e2){
				sum+=e1;
				lastt=i;
			}
			else{
				sum+=e2;
			}
		}
	}
	sum+=t[n]+a[n]*2;
	cout<<sum;
	return 0;
}