Seeking 1/1 - 1/2 + 1/3 - 1/4 + 1/5 - 1/6 + 1/7 - 1/8 + ... + (-1) n-1 · 1 value / n of .

Description questions

Programming, input the value of n, seeking 1/1 - 1/2 + 1/3 - 1/4 + 1/5 - 1/6 + 1/7 - 1/8 + ... + (-1) n value -1 · 1 / n of.

Input Format

Enter a positive integer n. 1 <= n <= 1000.

Output Format

Output a real number, the value of expression retained to four decimal places.

Sample input

2

Sample Output

0.5000

#include <stdio.h>
int main()
{
    int n,i;
    float a,sum;
    while(scanf("%d",&n)!=EOF)
    {
        sum=0; a=1;
        for(i=0;i<n;i++)
        {
            sum+=1/a;
            if(a>0)
            {
                a=-(a+1);
                continue; //此处如果没有continue，则会进入下一个if，达不到程序预期
            }
            if(a<0)
            {
                a=-(a-1);
                continue;
            }
        }
        printf("%.4f\n",sum);
    }
    return 0;
}