【CodeForces - 821C Okabe and Boxes】 思維+模擬

D - Okabe and Boxes

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.

Example

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.

題意：模擬棧的操作，給定兩種操作。

   add：向棧中加入一個數。

   remove：將棧頂的數彈出。

   現在要求使棧中的元素按照1-n的順序主次彈出，你可以在任意時刻將棧中的元素進行排序，問最少要進行多少次的排序。

分析：我們只需要在棧頂元素與所需彈出的元素不相同時進行一次排序，排序後可將棧內元素清空（因爲已經符合了之後要彈出的順序），記錄排序次數即可。

代碼如下：

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

#define LL long long
#define INF 0x3f3f3f3f

using namespace std;
const int MX = 3e5 + 5;
vector<int> vt;

int main(){
    int n;
    scanf("%d", &n);
    int cnt = 1, ans = 0;
    for(int i = 0; i < 2*n; i++){
        char op[10];
        scanf("%s", op);
        if(op[0] == 'a'){
            int x;
            scanf("%d", &x);
            vt.push_back(x);
        }
        else{
            if(!vt.empty()){
                if(vt.back() != cnt){
                    vt.clear();
                    ans++;
                    cnt++;
                }
                else{
                    vt.pop_back();
                    cnt++;
                }
            }
            else cnt++;
        }
    }
    printf("%d\n", ans);
    return 0;
}