# include <iostream>
# include <cstring>
using namespace std;

int cur = 0;
bool isp[100000010];
int prime[100000010];

void getprime()
{
    memset(isp, true, sizeof(isp));
    isp[0] = isp[1] = false;
    for (int i = 2; i <= 10000000; i++)
    {
        if (isp[i])
        {
            cur++;
            prime[cur] = i;
            for (int j = 2; i * j <= 10000000; j++)
            {
                isp[i * j] = false;
            }
        }
    }
    return;
}

int main()
{
    getprime();
    int n, ans = 0;
    cin >> n;
    for (int i = 1; i <= cur; i++)
    {
        if (prime[i] <= n)
            ans++;
        else
            break;
    }
    cout << ans;
    return 0;
}

最后两个点WA了，八十分