N = int(input())

p = [-1]*(N+1)
L = []
for i in range(2, N+1):
    if p[i] == 0:
        continue
    L.append(i)
    p[i] = 1
    for j in range(2*i, N+1, i):
        p[j] = 0

ans = -1
for r in L:
    if r**2-2 > N:
        break
    if p[r**2-2] == 1:
        ans += 2

print(max(0, ans))