#pragma GCC optimize("Ofast")

#include <bits/stdc++.h>

using namespace std;

#define int long long
#define x first
#define y second
#define File(a) freopen(a".in", "r", stdin), freopen(a".out", "w", stdout)

inline void debug() { cerr << '\n'; }
template<typename Type, typename... Other>
inline void debug(const Type& x, const Other&... y) { cerr << x << ' '; debug(y...); }
#define DEBUG(a...) cerr << "[" << #a << "] = ", debug(a);

typedef long long LL;
typedef pair<int, int> PII;

const int N = 2000010;
const int INF = 2e16;

template<typename Type>
inline void read(Type &res)
{
    res = 0;
    int ch = getchar(), flag = 0;
    while (!isdigit(ch)) flag |= ch == '-', ch = getchar();
    while (isdigit(ch)) res = (res << 3) + (res << 1) + (ch ^ 48), ch = getchar();
    res = flag ? -res : res;
}
template<typename Type, typename... Other>
inline void read(Type &res, Other&... y) { read(res), read(y...); }

int n;
PII a[N];
int f[N][21], dp[N];

void Init()
{
    for (int i = 1; i <= n; i ++) f[i][0] = a[i].y;
    for (int k = 1; k < 21; k ++)
        for (int i = 1; i + (1 << k) - 1 <= n; i ++)
            f[i][k] = max(f[i][k - 1], f[i + (1 << k - 1)][k - 1]);
}

inline int Query(int l, int r)
{
    int k = __lg(r - l + 1);
    return max(f[l][k], f[r - (1 << k) + 1][k]);
}

signed main()
{
    read(n);
    for (int i = 1; i <= n; i ++) read(a[i].x, a[i].y);
    Init();

    for (int i = 1; i <= n; i ++)
    {
        int l = 1, r = i - 1, res = 0;
        while (l <= r)
        {
            int mid = l + r >> 1;
            if (dp[mid] <= a[i].x) res = mid, l = mid + 1;
            else r = mid - 1;
        }
        dp[i] = a[i].x + 2 * Query(res + 1, i);
    }
    cout << dp[n] << '\n';

    return 0;
}