#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool c[2000001];

int main()
{
    int n,i,j,k=0;
    in>>n;
    for (i=2;i*i<=n;i++)
    {
        if(!c[i])
        {
            for (j=i*i;j<=n;j+=i)
            {
                c[j]=true;
            }
        }
    }
    for (i=2;i<=n;i++)
    {
        if(!c[i])
        {
            k++;
        }

    }
    out<<k;
    return 0;
}