#include <fstream>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

#define N 2000001

bool v[N];
long long n, cate;

int main()
{
    in >> n;
    for(long long i=2;i<=n;i++)
        if(v[i]==false)
        {
            cate++;
            for(long long j=i*i;j<=n;j+=i)
                v[j]=true;
        }

    out << cate;
    in.close();
    out.close();
    return 0;
}