JOE is on TV! CodeForces - 1293B（数学）

Our dear Cafe’s owner, JOE Miller, will soon take part in a new game TV-show “1 vs. n”!

The game goes in rounds, where in each round the host asks JOE and his opponents a common question. All participants failing to answer are eliminated. The show ends when only JOE remains (we assume that JOE never answers a question wrong!).

For each question JOE answers, if there are s (s>0) opponents remaining and t (0≤t≤s) of them make a mistake on it, JOE receives ts dollars, and consequently there will be s−t opponents left for the next question.

JOE wonders what is the maximum possible reward he can receive in the best possible scenario. Yet he has little time before show starts, so can you help him answering it instead?

Input
The first and single line contains a single integer n (1≤n≤105), denoting the number of JOE’s opponents in the show.

Output
Print a number denoting the maximum prize (in dollars) JOE could have.

Your answer will be considered correct if it’s absolute or relative error won’t exceed 10−4. In other words, if your answer is a and the jury answer is b, then it must hold that |a−b|max(1,b)≤10−4.

Examples
Input
1
Output
1.000000000000
Input
2
Output
1.500000000000
Note
In the second example, the best scenario would be: one contestant fails at the first question, the other fails at the next one. The total reward will be 12+11=1.5 dollars.
思路：一个比较简单的数学题吧，每次走一个人，最后的结果是最大的。
代码如下：

#include<bits/stdc++.h>
#define ll long long
using namespace std;int n;int main()
{while(~scanf("%d",&n)){double ans=0.0;for(int i=1;i<=n;i++) ans+=(double)(1.0/(i*1.0));printf("%.12lf\n",ans);}return 0;
}

努力加油a啊，(^o)/~

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JOE is on TV! CodeForces - 1293B（数学）

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