# 筛选出1-N中的质数
def get_prime(N):
    prime_vals = []
    flag = [True] * (N+1)
    for val in range(2, N+1):
        if flag[val]:
            prime_vals.append(val)
            for next_val in range(2*val, N+1, val):
                flag[next_val] = False

    return prime_vals

print(len(get_prime(int(input()))))