Codeforces 821C-Okabe and Boxes

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解决一个涉及盒子堆叠与移除的问题，通过模拟栈的操作来最小化重新排序次数，确保盒子按顺序被移除。

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Okabe and Super Hacker Daru are stacking and removing boxes. There are n boxes numbered from 1 to n. Initially there are no boxes on the stack.

Okabe, being a control freak, gives Daru 2n commands: n of which are to add a box to the top of the stack, and n of which are to remove a box from the top of the stack and throw it in the trash. Okabe wants Daru to throw away the boxes in the order from 1 to n. Of course, this means that it might be impossible for Daru to perform some of Okabe's remove commands, because the required box is not on the top of the stack.

That's why Daru can decide to wait until Okabe looks away and then reorder the boxes in the stack in any way he wants. He can do it at any point of time between Okabe's commands, but he can't add or remove boxes while he does it.

Tell Daru the minimum number of times he needs to reorder the boxes so that he can successfully complete all of Okabe's commands. It is guaranteed that every box is added before it is required to be removed.

Input

The first line of input contains the integer n (1 ≤ n ≤ 3·105) — the number of boxes.

Each of the next 2n lines of input starts with a string "add" or "remove". If the line starts with the "add", an integer x (1 ≤ x ≤ n) follows, indicating that Daru should add the box with number x to the top of the stack.

It is guaranteed that exactly n lines contain "add" operations, all the boxes added are distinct, and n lines contain "remove" operations. It is also guaranteed that a box is always added before it is required to be removed.

Output

Print the minimum number of times Daru needs to reorder the boxes to successfully complete all of Okabe's commands.

Examples

input
3
add 1
remove
add 2
add 3
remove
remove

output
1

input
7
add 3
add 2
add 1
remove
add 4
remove
remove
remove
add 6
add 7
add 5
remove
remove
remove

output
2

Note

In the first sample, Daru should reorder the boxes after adding box 3 to the stack.

In the second sample, Daru should reorder the boxes after adding box 4 and box 7 to the stack.

题意：模拟一个栈，有两种操作，栈顶增加一个元素，栈顶移除一个元素，要求元素按照编号大小移除，移除前可以选择是否调整栈内元素顺序，询问最少调整次数

解题思路：用vector模拟过程，遇到不满足时，将vector清空

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <algorithm>
#include <queue>
#include <vector>
#include <set>
#include <stack>
#include <map>
#include <climits>

using namespace std;

#define LL long long
const int INF = 0x3f3f3f3f;

int n, x;
char ch[30];

int main()
{
	while (~scanf("%d", &n))
	{
		vector<int>g;
		int ans = 0, cnt=1;
		for (int i = 1; i <= 2 * n; i++)
		{
			scanf("%s", ch);
			if (!strcmp(ch, "add"))
			{
				scanf("%d", &x);
				g.push_back(x);
			}
			else
			{
				if (g.empty());
				else if (g.back() == cnt) g.pop_back();
				else
				{
					ans++;
					g.clear();
				}
				cnt++;
			}
		}
		printf("%d\n", ans);
	}
	return 0;
}