#include <fstream>

using namespace std;

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

int n,nr,i,j;
bool v[20000002];

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

    return 0;
}