Cow Exhibition

"Fat and docile, big and dumb, they look so stupid, they aren't much fun..."

• Cows with Guns by Dana Lyons

The cows want to prove to the public that they are both smart and fun. To do this, Bessie has organized an exhibition that the cows will put on. She has given each of the $N$ ($1 \le N \le 100$) cows a thorough interview and determined two values for each cow: the smartness $S_i$ ($-1000 \le S_i \le 1000$) and the funness $F_i$ ($-1000 \le F_i \le 1000$) of cow $i$.

Bessie chooses which cows to bring to the exhibition. The total smartness $TS$ of the group is the sum of the $S_i$ values, and the total funness $TF$ is the sum of the $F_i$ values. Bessie wants to maximize $TS + TF$, but both $TS$ and $TF$ must be non-negative. Help her maximize $TS + TF$ without letting either value become negative.

The first line contains a single integer $N$, the number of cows. Each of the next $N$ lines contains two space-separated integers $S_i$ and $F_i$, the smartness and funness of cow $i$.

Print one integer: the maximum value of $TS + TF$ such that both $TS$ and $TF$ are non-negative. If no subset of cows has non-negative $TS$ and non-negative $TF$, print $0$.

Bessie chooses cows 1, 3, and 4, giving $TS = -5 + 6 + 2 = 3$ and $TF = 7 - 3 + 1 = 5$, so $TS + TF = 8$. Adding cow 2 would raise $TS + TF$ to 10, but $TF$ would become negative, so that choice is not allowed.