#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=1e5+5,inf=1e15+7;  
int n,a[N],t[N],mx[N],f[N];
signed main(){
	freopen("a.in","r",stdin);
	freopen("a.out","w",stdout);
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	cin>>n;for(int i=1;i<=n;++i) cin>>t[i]>>a[i];t[n+1]=inf;
	for(int i=1;i<=n;i++){
		int mx=a[i];f[i]=inf;for(int j=i-1;j>=0;j--){if(f[j]<t[i+1]) f[i]=min(f[i],max(f[j],t[i])+2*mx);mx=max(mx,a[j]);}
	}
	cout<<f[n]<<"\n";
	return 0;
}