list=[1,2,3,4,5,6,7,8,9,10]
high=len(list)
low=0
x=int(input())
def binary_search(list,item):
low=0
high=len(list)-1
while low<=high:
mid=int((low+high)/2)
guess=list[mid]
if guess==item:return mid
if guess>item:
high=(mid-1)
else:
low=mid+1
return 0
print(binary_search(list,x))
