#include <iostream>
#include <fstream>
using namespace std;

int p[2000001];
int main()
{
    int n,nr=0,i,j;

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

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

    return 0;
}