#import<fstream>

char p[2000010];

main()
{
    int n; std::ifstream("ciur.in")>>n;

    int i, j, r = 0;

    for(i = 2; i <= n; ++i)
    {
        if(p[i] == 0)
        {
            r++;

            for(j = i + i; j <= n; j += i)
            {
                p[j] = 1;
            }
        }
    }

    std::ofstream("ciur.out")<<r;
}