#include <iostream>
#include <cstdio>
using namespace std;

typedef long long ll;
const int N = 2000010;
int t[N], a[N], n, nxtmax[N];

int main() {
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) 
        scanf("%d%d", &t[i], &a[i]);
    ll ans = 0;
    ll maxv = 0, maxid;
    for (int i = n; i; i--) {
        if(a[i] > maxv) {
            maxid = i;
            maxv = a[i];
        }
        nxtmax[i] = maxid;
    }
    ll nowt = 0;
    for (int pos = 1; pos <= n; ) {
        pos = nxtmax[pos];
        nowt = max(nowt, 1ll * t[pos]);
        int nxt = pos;
        while(nxt <= n && t[nxt] <= nowt) nxt++;
        nowt = nowt + a[pos] * 2ll;
        ans = max(ans, nowt);
        pos = nxt;
    }
    printf("%lld\n", ans);
    return 0;
}