【1】【二分搜索】CodeForces 650B Image Preview

B. Image Preview

time limit per test:1 second

memory limit per test:256 megabytes

input:standard input

output:standard output

Vasya’s telephone contains n photos. Photo number 1 is currently opened on the phone. It is allowed to move left and right to the adjacent photo by swiping finger over the screen. If you swipe left from the first photo, you reach photo n. Similarly, by swiping right from the last photo you reach photo 1. It takes a seconds to swipe from photo to adjacent.

For each photo it is known which orientation is intended for it — horizontal or vertical. Phone is in the vertical orientation and can’t be rotated. It takes b second to change orientation of the photo.

Vasya has T seconds to watch photos. He want to watch as many photos as possible. If Vasya opens the photo for the first time, he spends 1 second to notice all details in it. If photo is in the wrong orientation, he spends b seconds on rotating it before watching it. If Vasya has already opened the photo, he just skips it (so he doesn’t spend any time for watching it or for changing its orientation). It is not allowed to skip unseen photos.

Help Vasya find the maximum number of photos he is able to watch during T seconds.

Input

The first line of the input contains 4 integers n, a, b, T (1 ≤ n ≤ 5·105, 1 ≤ a, b ≤ 1000, 1 ≤ T ≤ 109) — the number of photos, time to move from a photo to adjacent, time to change orientation of a photo and time Vasya can spend for watching photo.

Second line of the input contains a string of length n containing symbols ‘w’ and ‘h’.

If the i-th position of a string contains ‘w’, then the photo i should be seen in the horizontal orientation.

If the i-th position of a string contains ‘h’, then the photo i should be seen in vertical orientation.

Output

Output the only integer, the maximum number of photos Vasya is able to watch during those T seconds.

Examples

input

4 2 3 10

wwhw

output

2

input

5 2 4 13

hhwhh

output

4

input

5 2 4 1000

hhwhh

output

5

input

3 1 100 10

whw

output

0

Note

In the first sample test you can rotate the first photo (3 seconds), watch the first photo (1 seconds), move left (2 second), rotate fourth photo (3 seconds), watch fourth photo (1 second). The whole process takes exactly 10 seconds.

Note that in the last sample test the time is not enough even to watch the first photo, also you can’t skip it.

链接

CodeForces 650B

题意

在手机里面左右翻照片。手机是固定的，w表示照片要旋转，用时b秒，h表示不用转。关键是第一张往右滑就是最后一张，最后一张往左滑就是第一张。每张新照片要看1秒钟，看过的照片不会再看，即不会在花费1秒。照片滑动到相邻的一张要a秒，问T时间内最多可以看几张。

分析

16/8/10由于本来没读懂上面加粗的部分，所以不知道这道题有最优情况。看了网上的题解有两种代码实现方法，我目前学了扩大数组的那种。l和r分别表示往左看到哪一张和往右看到哪一张，过程中还有一些细节也要注意。