#include<iostream>
#include<cstdio>
#include<algorithm>
#define int long long
using namespace std;
const int mn=2e6+5;
int n;
int a[mn],b[mn];
int c[mn],d[mn],tp;
int f[mn];
signed main()
{
    int x,y;
    scanf("%lld",&n);
    // tp=1;
    for(int i=1;i<=n;i++)
    {
        scanf("%lld%lld",&a[i],&b[i]);
        if(tp!=0 && b[i]>=b[i-1])
        {
            c[tp]=a[i];
            d[tp]=b[i];
        }
        else
        {
            tp++;
            c[tp]=a[i];
            d[tp]=b[i];
        }
    }
    for(int i=1;i<=tp;i++)
    {
        // scanf("%lld%lld",&a[i],&b[i]);
        x=d[i];
        f[i]=0x3f3f3f3f3f3f3f3f;
        for(int j=i-1;j>=0;j--)
        {
            f[i]=min(f[i],max(f[j],c[i])+x*2);
            x=max(x,d[j]);
        }
    }
    printf("%lld",f[tp]);
    return 0;
}