codeforces821 C（栈操作）

C. Okabe and Boxes

time limit per test

3 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

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

3add 1removeadd 2add 3removeremove

output

1

input

7add 3add 2add 1removeadd 4removeremoveremoveadd 6add 7add 5removeremoveremove

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.

给你两种操作，一种是将某个数字加入栈中，另一种是取出栈顶数字，要求取出的数字顺序按1到n的顺序，给你一系列操作，你可以在任何一次操作后对栈中序列进行重排，可以排成任意顺序，问最少需要进行多少次重排才能满足条件

思路：直接进行栈操作，当栈中元素满足栈顶顺序为1-n时候，栈顶元素一一弹出，当栈不为空并且不满足1-n顺序时，ans++，将栈清空。

代码：

#include<bits/stdc++.h>
using namespace std;
const int maxn=3e5+5;
int main()
{
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        string s;
        stack<int>q;
        int x;
        int num=0;
        int ans=0;
        int count=0;
        for(int i=0;i<n*2;i++)
        {
            cin>>s;
            if(s[0]=='a')
            {
                scanf("%d",&x);
                q.push(x);
            }
            else
            {
                num++;
                if(!q.empty()&&q.top()==num)
                {
                  q.pop();
                }
                else if(!q.empty())
                {
                    ans++;
                    while(!q.empty())
                    {
                        q.pop();
                    }
                }
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}