#include <iostream>
#include <fstream>

using namespace std;
ifstream in ("ciur2.in");
ofstream out ("ciur2.out");

bool v[2000000];

void makeciur (int n)
{
    int i , j;

    v[0]=v[1]=1;

    for (i=2; i<=n; i++)
    {
        if (v[i]==0)
        {
          for(j=2*i; j<=n; j=j+i)
          {
              v[j]=1;
          }
        }
    }
}

int main()
{
    int n, i, rez=0;
    in>>n;
    makeciur(n);
    for (i=1; i<=n; i++)
    {
        if(v[i]==0)
        {
            rez++;
        }
    }
    out<<rez;
    return 0;
}