from random import *
from math import *

def X():
    a=randint(-2,2)
    x=a**2
    return x

def Moyenne(n):
    somme=0
    for i in range(n):
        somme=somme+X()
    m=somme/n
    return m

def Ecart_type(n,N):
    e=2
    v=0
    for j in range(N):
        v=v+(Moyenne(n)-e)**2
    v=v/N
    s=sqrt(v)
    return s