from math import *

def Combi(n,k):
    C=factorial(n)//(factorial(k)*factorial(n-k))
    return C

def Seuil(S):
    k=0
    P=0.95**80
    while P<S:
        k=k+1
        P=P+Combi(80,k)*0.05**k*0.95**(80-k)
    return k