#include <bits/stdc++.h>
using namespace std;

const int N = 2e3 + 5;

int n;

struct Node{
    int s,t;
}a[N];

long long f[N];

int g[N][N];

int main(){
    cin >> n;
    for (int i = 1;i <= n;i++)
        cin >> a[i].t >> a[i].s;
    for (int i = 1;i <= n;i++){
        g[i][i] = a[i].s;
        for (int j = i + 1;j <= n;j++)
            g[i][j] = max(g[i][j - 1],a[j].s);
    }
    for (int i = 1;i <= n;i++) f[i] = LONG_LONG_MAX;
    for (int i = 1;i <= n;i++){
        for (int j = 1;j <= i;j++){
            f[i] = min(f[i],max(f[j - 1],1ll * a[i].t) + g[j][i] * 2);
            // cout << j << ' ' << i << ':' << g[j][i] << '\n';
        }
    }
    cout << f[n];
    return 0;
}