#include <stdio.h>
#include <math.h>
int main()
{
int i, n;
double item, sum;
while (scanf("%d", &n) != EOF)
{
sum = 0;
for (i = 1; i <= n; i++)
{
item = sqrt(i);
sum = sum+item;
}
printf("sum = %.2f\n", sum);
}
return 0;
}