Accumulator Apex

目前有一个数 $x$ 与 $k$ 个数列。 每次操作，都可以取这 $k$ 个数列中的头一个元素，然后将 $x$ 加上这个元素。在这个过程中 $x$ 始终非负。 求 $x$ 能够达到的最大值。

Allyn is playing a new strategy game called "Accumulator Apex". In this game, Allyn is given the initial value of an integer $ x $ , referred to as the accumulator, and $ k $ lists of integers. Allyn can make multiple turns. On each turn, Allyn can withdraw the leftmost element from any non-empty list and add it to the accumulator $ x $ if the resulting $ x $ is non-negative. Allyn can end the game at any moment. The goal of the game is to get the largest possible value of the accumulator $ x $ . Please help Allyn find the largest possible value of the accumulator $ x $ they can get in this game.

The first line of the input contains two integers $ x $ and $ k $ ( $ 0 \leq x \leq 10^9, 1 \leq k \leq 10^5 $ ) — the initial value of the accumulator $ x $ and the number of lists. The next $ k $ lines contain the description of lists: an integer $ l_i $ ( $ l_i \ge 1 $ ) followed on the same line by $ l_i $ elements of the list in the order from left to right. Each element of lists does not exceed $ 10^9 $ by the absolute value, and the total size of all lists does not exceed $ 10^5 $ .

The sole line of the output should contain the largest value of the accumulator $ x $ Allyn can get.

1 3
2 -1 2
2 -2 3
2 -3 4

4

1 2
3 -1 -1 4
4 1 -3 -4 8

4

In the first input, we start with $ x = 1 $ . Then, we can take the first integer from the first list and get $ x = 0 $ — adding the next integer $ 2 $ from the first list we get $ x = 2 $ . After that, we can add the integers from the second list and obtain $ x = 3 $ . Finally, we can add the integers from the third list and obtain $ x = 4 $ . In the second input, we can add the first integer from the second list and get $ x = 2 $ . Then, by adding the elements from the first list, we get $ x = 4 $ . We cannot add more integers to increase $ x $ .