#import<fstream>

char p[2000010];

int sieve1(int n)
{
    int i, j, nr = 0;

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

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

    return nr;
}

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

    std::ofstream("ciur.out")<<sieve1(N);
}