#include <iostream>
#include <fstream>

using namespace std;

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

int n,d,i,j,Q;
char v[2000001];

int main()
{
    in>>n;
    for (i=2;i<=n;i++)
    {
        if(v[i] == 0)
        {
            for (j=i*2;j<=n;j=j+i)
                v[j]=1;
        }
    }
    for (i=2;i<=n;i++)
        if ( v[i]==0 ) Q++;
    out<<Q;
    return 0;
}