#include <stdio.h>

int main()

{

    double sum = 0; double j = 1.0;

    for (int i = 1; i <= 100; i++)

    {

        if (i % 2 == 1)

        {

            sum = 1.0 / j + sum; j = j + 1.0;

        }

        else

        {

            sum = sum - 1.0 / j;

            j = j + 1.0;

        }

    }

    printf("%f", sum);

    return 0;

}