题解 | #牛牛学数列3#

#include <stdio.h>

int main() {
    int input;
    int j1=-1;
    int j2;
    int sum=0;
    double all=0;
    scanf("%d",&input);
    for(int i=1;i<=input;i++)
    {
        j1=j1+2;
        j2=j1;
        if(i%2==0)
        {
            j2=-j1;
        }
        sum=sum+j2;
        all=all+1.0/sum;
    }
    printf("%.3lf",all);
    return 0;
}