Okabe and Boxes（CodeForces - 821C ）（模拟栈）

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

Copy

3
add 1
remove
add 2
add 3
remove
remove

output

Copy

1

input

Copy

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

output

Copy

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

有两种操作，一种是将某个数字加入栈中，另一种是取栈顶数字，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

重排肯定是排成小的在上大的在下的样子，我们不需要真的模拟，在遇到要重排的时候可以直接清空栈，而统计重排次数的时候只是在栈不为空且栈顶不是需要弹出的那个值的时候统计，并且清空

#include
#include
using namespace std;
stackst;
char op[10];
int main()
{
    int n,x,ans,cur;
    scanf("%d",&n);
   // getchar();
    cur=0;
    ans=0;
    for(int i=0;i<2*n;i++)
    {
        scanf("%s",op);
        if(op[0]=='a')
        {
            scanf("%d",&x);
            st.push(x);
        }
        else
        {
            cur++;
            if(!st.empty()&&st.top()==cur)
            {
                st.pop();
            }
            else if(!st.empty())
            {
                    ans++;
                    while(!st.empty())
                        st.pop();
            }
        }
    }
    printf("%d\n",ans);
    return 0;
}