#include <fstream>
#include <string>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n, cnt;
bool v[1000005];

int main()
{
    fin>>n;
    for (int i=2; i<=n; ++i)
    {
        v[i]=1;
    }
    for (int i=2; i<=n; ++i)
    {
        if (v[i])
        {
            cnt++;
            for (int j=i+i; j<=n; j+=i)
            {
                v[j]=0;
            }
        }
    }
    fout cnt;

    return 0;
}