A. Save Luke
题目连接：
http://codeforces.com/contest/624/problem/A
Description
Luke Skywalker got locked up in a rubbish shredder between two presses. R2D2 is already working on his rescue, but Luke needs to stay alive as long as possible. For simplicity we will assume that everything happens on a straight line, the presses are initially at coordinates 0 and L, and they move towards each other with speed v1 and v2, respectively. Luke has width d and is able to choose any position between the presses. Luke dies as soon as the distance between the presses is less than his width. Your task is to determine for how long Luke can stay alive.
Input
The first line of the input contains four integers d, L, v1, v2 (1 ≤ d, L, v1, v2 ≤ 10 000, d < L) — Luke's width, the initial position of the second press and the speed of the first and second presses, respectively.
Output
Print a single real value — the maximum period of time Luke can stay alive for. Your answer will be considered correct if its absolute or relative error does not exceed 10 - 6.
Namely: let's assume that your answer is a, and the answer of the jury is b. The checker program will consider your answer correct, if .
Sample Input
2 6 2 2
Sample Output
1.000000
Hint
题意
有一个长度为L的通道，左右各有一人来抓你，速度分别是V1，V2，你的宽度是D，然后问你，你最多能存活多久
题解：
直接用(l-d)/(v1+v2)就好了，不用去管你究竟站哪儿，最久肯定是左右跑一样的时间的时候
代码
#include<bits/stdc++.h>
using namespace std;
int main()
{
double d,l,v1,v2;
cin>>d>>l>>v1>>v2;
printf("%.12f\n",(l-d)/(v1+v2));
}