#include <fstream>
#include <iostream>

using namespace std;

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

#define MAX 2001000

bool a[MAX+19];

int main()
{
    int n,i,j,k;
    a[0]=a[1]=1;
    fin>>n;
    k=0;
    for(i=2;i<=n;i++)
    {
        if(!a[i])
        {
            for(j=i*i;j<=MAX;j+=i)
                a[j]=1;
            k++;
        }
    }
    fout<<k<<"\n";

    return 0;
}