import math  
import sys  
  
def sd_calc(data):  
    n = len(data)  
  
    if n <= 1:  
        return 0.0  
  
    mean, sd = avg_calc(data), 0.0  
  
    # calculate stan. dev.  
    for el in data:  
        sd += (float(el) - mean)**2  
    sd = math.sqrt(sd / float(n-1))  
  
    return sd  
  
def avg_calc(ls):  
    n, mean = len(ls), 0.0  
  
    if n <= 1:  
        return ls[0]  
  
    # calculate average  
    for el in ls:  
        mean = mean + float(el)  
    mean = mean / float(n)  
  
    return mean  
  
data = [4, 2, 5, 8, 6]  
print("Sample Data: ",data)  
print("Standard Deviation : ",sd_calc(data))