#include <bits/stdc++.h>  
using namespace std;  
long long n,top,a[100005],b[100005],cur,dp[100005];  
int main(){ 
	freopen("a.in","r",stdin);
	freopen("a.out","w",stdout);
    cin >> n;  
    for (long long i = 1; i <= n; i++) {  
        cin>>a[i]>>b[i];  
    }  
    memset(dp,100,sizeof(dp));  
    dp[0]=0;  
    for (long long i = 1; i <= n; i++) {  
        long long maxx = b[i];  
        for (long long j = i - 1; j >= 0; j--) {  
            if (dp[j]<a[i]) {  
                dp[i]=min(dp[i],a[i]+maxx*2);  
            } else {  
                dp[i]=min(dp[i],dp[j]+maxx*2);  
            }  
            maxx=max(maxx,b[j]);  
        }  
    }  
    cout<<dp[n];
    return 0;  
}