from sys import stdin
from sys import exit
##  input functions for me
def ria(sep = ''):
    if sep == '' :
        return list(map(int, input().split())) 
    else: return list(map(int, input().split(sep)))
def rsa(sep = ''):
    if sep == '' :
        return input().split() 
    else: return input().split(sep)
def ri(): return int(input())
def rd(): return float(input())
def rs(): return input()
##

## main ##

N = ri()
isPrime = [True] * (N + 1)
isPrime[0] = False
isPrime[1] = False
P = []
for i in range(2,N+1):
    if not isPrime[i]: continue
    P.append(i)
    for j in range(i + i, N + 1, i): isPrime[j] = False

ans = 0
if N == 1:
    print(0)
    exit(0)

for r in P:
    p = 2
    q = r * r - p
    if q >= 0 and q <= N and isPrime[q]: ans += 2

ans -= 1
print (ans)