N = int(input())

prime = set()
dat = [0] * (N + 1)

for i in range(2,N + 1):
    if dat[i] == 0:
        prime.add(i)
        for j in range(i * 2,N + 1,i):
            dat[j] = 1
ans = 0

if N >= 2:
    ans -= 1
count = 0
for r in prime:
    if r ** 2 - 2 in prime:
        count += 1
print(ans + count * 2)