#include<stdio.h>
#include<math.h>

int main() {
   int n, i;
   double difference, realSum, currentSum = 0;
   scanf("%d", &n);
   for (i = 1; i / 2 <= n; i = i + 2){
       currentSum = currentSum + 1.0 / (i * (i + 1) * (i + 2));
   }
   realSum = log(2.0) - 1.0/2.0;
   difference = realSum - currentSum;
   printf("the difference between the total sum and the sum of the first %d terms is %f", n, difference);
   return 0;
}