CF - 652A. Gabriel and Caterpillar 模拟+思维

1.题目描述：

A. Gabriel and Caterpillar

time limit per test
1 second

memory limit per test
256 megabytes

input
standard input

output
standard output

The 9-th grade student Gabriel noticed a caterpillar on a tree when walking around in a forest after the classes. The caterpillar was on the
height h1 cm
from the ground. On the height h2 cm
(h2 > h1)
on the same tree hung an apple and the caterpillar was crawling to the apple.

Gabriel is interested when the caterpillar gets the apple. He noted that the caterpillar goes up by a cm per hour by day and slips
down by bcm per hour by night.

In how many days Gabriel should return to the forest to see the caterpillar get the apple. You can consider that the day starts at 10 am and
finishes at 10 pm. Gabriel's classes finish at 2 pm.
You can consider that Gabriel noticed the caterpillar just after the classes at 2 pm.

Note that the forest is magic so the caterpillar can slip down under the ground and then lift to the apple.

Input

The first line contains two integers h1, h2 (1 ≤ h1 < h2 ≤ 105)
— the heights of the position of the caterpillar and the apple in centimeters.

The second line contains two integers a, b (1 ≤ a, b ≤ 105)
— the distance the caterpillar goes up by day and slips down by night, in centimeters per hour.

Output

Print the only integer k — the number of days Gabriel should wait to return to the forest and see the caterpillar getting the apple.

If the caterpillar can't get the apple print the only integer  - 1.

Examples

input

10 30
2 1

output

1

input

10 13
1 1

output

0

input

10 19
1 2

output

-1

input

1 505 4

output

1

Note

In the first example at 10 pm of the first day the caterpillar gets the height 26.
At 10 am of the next day it slips down to the height 14.
And finally at 6 pm of the same day the caterpillar gets the apple.

Note that in the last example the caterpillar was slipping down under the ground and getting the apple on the next day.

2.题意概述：

有一个虫刚开始在h1的高度,有个苹果在h2的高度,已知其白天每小时爬a米,夜晚滑落b米每小时.  并且规定白天时间是10~22.有个小孩每天2点下课.他想看到虫吃到苹果的场景,问第几天他能看到？ 

3.解题思路：

理清楚关系的话典型的模拟，注意的点一个是如果下降高度比爬高度还多，则直接判断第一天是否能到达目的地，不能则-1，之后的情况直接判断毛毛虫是否在下午两点以后到达即可

4.AC代码：

#include <stdio.h>
using namespace std;
int h1, h2, a, b;

int main()
{
scanf("%d%d%d%d", &h1, &h2, &a, &b);
if (a <= b)
{
if (h1 + 8 * a < h2)
{
puts("-1");
return 0;
}
}
if (h1 + 8 * a >= h2)
{
puts("0");
return 0;
}
int h = h2 - h1 - 8 * a;
int d = (a - b) * 12;
int ans = h / d;
if (h % d)
ans++;
printf("%d\n", ans);
return 0;
}