#include <stdio.h>
int main()
{
int numerator, denominator, flag, i, n;
double item, sum;
while (scanf("%d", &n) != EOF)
{
flag = 1;
numerator = 1;
denominator = 1;
sum = 0;
for (i = 1; i <= n; i++)
{
item = flag*1.0*numerator/denominator;
sum = sum+item;
flag = -flag;
numerator = numerator+1;
denominator = denominator+2;
}
printf("%.3f\n", sum);
}
return 0;
}