#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;

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

int v[2000000],cont;
int main()
{
    int n,i,j;
    f>>n;
    for(i=2;i<=n;i++)
        if(v[i]==0)
        {
            cont++;
            for (j=i+i;j<=n;j=j+i)
                v[j]=1;
        }
    g<<cont;
    return 0;
}